This case report describes the clinical findings, treatment and outcome of a four-year-old goat with type I diabetes mellitus. Weight loss, polydipsia and polyuria were the main clinical signs. Urinalysis revealed glucosuria, ketonuria and aciduria. The most important haematological and biochemical findings were anaemia attributable to parasitism, hyperglycaemia and hypoinsulinaemia. The goat was treated with insulin administered subcutaneously twice daily for almost four years. The goat developed bronchopneumonia at eight years of age and was euthanased. Postmortem examination showed degeneration of insulin-producing beta-cells of the pancreas.