Many diabetic patients suffer from some degree of periodontal disease, one of the most regular pathologic conditions in veterinary practice. Studies in humans exhibit that risk and rate of periodontitis progression are altered in diabetic patients for reasons related to glycation of proteins, microvascular injury, reduced leukocytes function, poorer cicatrization, and major collagen reabsorption. Nevertheless, this relationship between periodontitis and diabetes is a two side coin. The evidence shows that periodontal diseases can contribute to poorer glycemic control in people with diabetes due to higher IL-1 and TNF-a levels in trabecular fluids and serum of people with periodontitis. No study on this subject was found in veterinary literature. The aim of this work is report one case of a thirteen years old female Poodle with diabetes diagnosis more than one year ago, concomitant with mild periodontal disease. The glycemic control was stable by use of high fiber diet and human NPH insulin (3U) twice in day. Last fructosamine concentration was 318μmol/L. Owner was monitoring glycosuria every days, founding normally negative results or glucose traces. Suddenly, owner reports glycosuria increase (three to four crosses) and polyuria/polydipsia along the last three days. Oral examination show up severe periodontal reaction with severe gingival hyperemia, calculus and furcation involvement. Marked neutrophilia, glycemia 419 mg/dL after two hours and 326 mg/dL after ten hours of insulin application and fructosamine concentration 379 μmol/L were some laboratorial findings. Others parameters were between reference range. Serum cortisol post eight hours from 0.01 mg/kg IV dexamethasone was 0.32 μg/dL and abdominal ultrasonography shows no abnormalities. Insulin dosage was increased for 4U and active periodontal diagnosis was made. The patient was submitted to oral prophylaxis after three days on routine antibiotic therapeutics with eighteen teeth extraction. Ten days after surgery, sustain antibiotic therapy and daily 0.2% chlorhexidine cleaning, owner reported an hypoglycemic episode with muscular shake. Insulin dosage was reduced to 3U again and the dog maintained normoglycemia detected by negative to traces of glucose in urine reported every day since then. This work reports clear occurrence and resolution of insulin resistance in a dog due to severe periodontitis and concurrent treatment respectively.