Background and objectives: Diabetes mellitus (DM) is a common endocrinopathy in dogs, but only few studies described laboratory changes in diabetic dogs and current knowledge is mainly derived from textbooks. In addition, information on epidemiology and management in general practice is limited, and no current data concerning diabetic dogs in Germany can be found in the literature. The aim of this study was therefore to evaluate retrospectively laboratory changes and epidemiological data based on laboratory submissions to a large commercial veterinary laboratory, as well as prospectively collect information on management and treatment of DM in Germany. Such information might guide future recommendations concerning management of canine DM in Germany. Material and methods: The basis of the retrospective examination was the dataset of 145072 records from 2015 to 2018, provided by the commercial veterinary laboratory SYNLAB Vet. Fructosamine was used to distinguish diabetic (? 370 µmol/l) from non-diabetic dogs as well as to differentiate between good (370 – 450 µmol/l) and bad (> 450 µmol/l) glycaemic control of diabetic dogs. Besides the evaluation of epidemiological data (prevalence, age, gender and neutering status) and selected laboratory geriatric profile data (haematology, clinical chemistry, total thyroxine) were compared between groups. Non-parametric tests and effect size measures were used to examine the relevance of the identified differences. In the prospective part of this investigation between April 2021 and December 2022, DGGR lipase and vitamin B12 concentrations of 54 diabetic dogs in Germany were evaluated in addition to the selected laboratory parameters of the geriatric profile. Data on signalment, age at DM diagnosis, current and former nutritional status and seasonality of DM diagnosis as well as medical management (insulin type and dose, diet and feeding practices, quality of diabetic control, concomitant diseases and complications) were obtained from questionnaires submitted alongside blood samples. ? Results: The prevalence of canine DM was 5.12 % (confidence interval 5.01 – 5.24 %). Median age of diabetic dogs was 9 (interquartile range 6 – 12) years in the retrospective population and 10 (8 – 12) years at the time of study participation in the prospective cohort (median age at DM diagnosis was 9 [7.8 – 10.7] years). In the retrospective part, male intact and female intact dogs were significantly (p < 0.001) more frequently diabetic than male castrated and female castrated dogs. However, these differences did not reach relevance based on measures of effect sizes (Cramér V = 0.026). Mixed breed dogs (18/50; 36 %) and terriers (9/30; 30 %) were most frequently affected in the prospective study cohort. Median weight upon study participation was 11.7 kg (7.3 – 22.5 kg) (N: 47), with 43 % (21/49) of dogs having normal body condition score (4 – 5/9). The most common season of DM diagnosis was winter (18/47; 38 % diagnosed December-February) for the whole study cohort, and spring (4/7; 57 % diagnosed March – May) when only intact female dogs were considered. At the time of prospective study participation, most diabetic dogs had been receiving insulin for 1 – 6 months (16/53; 30 %) and Caninsulin (MSD Animal Health) was the most common insulin preparation (35/42; 83 %). The median insulin dose was 1.0 IE/kg/day (0.7 – 1.4 IE/kg/day) and in most diabetic dogs their disease was poorly regulated (39/51; 76.5 %) based on the questionnaires (i.e., based on veterinarian / owner opinion). There was no significant difference (p = 0.121) between the evaluation of the quality of diabetic control as reported in the questionnaire and based on fructosamin concentration (cut off > 450 µmol/l). Diabetic diets were only offered to 58 % (31/53) of dogs, and most diabetic dogs received food twice daily (44/53; 83 %). Fructosamin was most frequently (27/49; 55 %) used to make insulin dose adjustments, and in 49 % (24/49) of dogs, more than one glycaemic parameter (including clinical signs) was used. For those diabetic dogs with poor glycaemic control, this assessment was usually made based on more than one parameter (30/38; 79 %), with polyuria/polydipsia being the most common criterion (25/38; 66 %). Complications of DM were present in 50 % (27/54) of diabetic dogs and diabetic cataract was the most frequent (18/54; 33 %). Concomitant diseases (29/54; 54 %), especially pancreatitis (14/54; 26 %), were common, too. Gastrointestinal symptoms (excluding weight loss) were present in 10/54 (19 %) dogs. In the retrospective study, the most relevant laboratory finding was an increase in alkaline phosphatase (AP) (p < 0.001; r = 0.405 for the absolute values; p < 0.001 and Cramér V = 0.257 for the fivefold increased AP) in poorly regulated diabetic dogs. Increased DGGR lipase > 213 U/l was present in 24.5 % (13/53) and low cobalamin < 295 pmol/l in 9.6 % (5/52) of diabetic dogs in the prospective study. ? Conclusions: The high DM prevalence found in this study was most likely due to the study design, including only dogs presented to veterinarians for blood sampling, and is therefore presumably higher than the true prevalence of DM in German dog population. Similar to other publications, diabetic dogs were middle aged. There was no clinically relevant DM predisposition based on gender or neutering status. Management of DM concerning insulin treatment and feeding in German diabetic dogs mostly complies with the international guidelines. The relatively frequent use of frucosamine measurements to adjust insulin dose, which has been used even more frequently than blood glucose curves, however, provides an aspect for further improvement. Because there were significant and relevant differences in AP activity between well and poorly regulated diabetic dogs, high AP activity might be a useful marker of poor diabetic control. Thus, re-evaluation of diabetic control should be considered if there is an increased AP in supposedly well-controlled diabetics. This study represents the first publication of epidemiological and laboratory data from diabetic dogs in German general practice and might provide the basis for future development of recommendations and guidelines concerning the monitoring and treatment of canine DM, adapted to the situation in German veterinary practices.