¹Ondokuz Mayıs University, Faculty of Veterinary Medicine, Department of Obstetrics and Gynecology, TR-55139 Samsun - TURKEY DOI : 10.9775/kvfd.2020.23865 Pyometra, a diestrus period disorder with a long term of progesterone exposure to endometrium, is a common disease of nulliparous female dogs. Closed-cervix pyometra is an emergency medical condition that requires rapid intervention. The possibility of treatment is further limited when associated with a chronic disease such as diabetes. This case describes a closed cervix pyometra in a 4-year-old bitch with comorbid diabetes mellitus and long-term contraceptive therapy. Closed-cervix pyometra was diagnosed and confirmed by ultrasound examination typical of pyometra, vaginal smear indicating diestrus and serum progesterone level (52 ng/mL). Serum fructosamine level was 475 μmol/L, interpreting diabetes mellitus. Treatment included ovariohysterectomy and normoglycemia was achieved with glargine insulin. Although, reproductive hormones and diestrus are associated with Type II diabetes mellitus in bitches, there are no reports limited to our search, on pyometra concomitant with diabetes mellitus except Elkhounds. Since the situation has a vital clinical importance, this report aims to emphasize the insidious diabetes mellitus development potential and treatment in canine pyometra which is usually misdiagnosed or unconsidered in clinical practice. Keywords : Dog, Diabetes mellitus, Pyometra