Tumours of the apocrine glands of the anal sac represent 2% of all canine skin and subcutaneous tumours, and 17% of all perianal malignancies. Most tumours are malignant (adenocarcinoma) with 46-90% of tumours having spread at time of diagnosis. Early diagnosis, aggressive surgery and adjunctive therapy are crucial in achieving the best possible outcome for an individual patient. In this review, Katie McNaught and Professor Jo Morris of the College of Medical, Veterinary and Life Sciences aim to highlight the clinical signs and importance of early diagnosis and staging and discuss the different treatment options available.