Анотация: An eight year old female spayed 5 kg mix breed dog was presented with a 3 month history of a skin ulcer that first occurred 5 days after administration of an imidacloprid spot-on formulation. The dog also had erosive and crusted lesions on the dorsum and head, a firm nodule on the tongue and an ocular infection. The rest of the physical examination was un-remarkable. Blood work showed a neutrophilia, hypoalbuminemia, hypercholesterolemia and an elevated alkaline phosphatase activity. Serum cortisol levels were 4.74 мg/dl before and 20.6 мg/dl after ACTH administration. Cytology of the skin lesions showed neutrophils, macrophages and cocci. Biopsy showed a pyogranulomatous dermatitis and panniculitis. The dog`s general condition deteriorated and it died. Necropsy revealed pus in the subcutaneous adipose tissue and the mesentery, and a pyogranulomatous reaction in the lungs, liver and heart. No organisms were detected with special stains. To the best of the author`s knowledge this is the first reported observation of a possible association between imidacloprid application and a pyogranulomatous reaction