Treatment of anal furunculosis in dogs is often unsatisfactory and may be associated with significant recurrence and complications. This may be compounded by the simultaneous presence of colitis in affected animals. Clinical signs associated with colitis and anal furunculosis may be similar, including faecal tenesmus, dyschezia and haematochezia. To examine the incidence of concurrent anal furunculosis and colitis, colonic biopsies were collected from 18 dogs referred for treatment of anal furunculosis. Nine dogs (50 per cent) had a histopathological diagnosis of colitis. Clinical signs more indicative of colitis than anal furunculosis (increased frequency of defecation, mucus in faeces and diarrhoea) were not observed more frequently in dogs with confirmed colitis compared with those with furunculosis alone. Therefore, while an association between colitis and anal furunculosis may exist, clinical signs alone cannot be used as an indicator of the presence of colitis in cases of anal furunculosis. The authors recommend that colonic biopsies should be undertaken in all dogs presented with anal furunculosis. Whether specific treatment of colitis in dogs with histopathological evidence of colitis improves the outcome of treatment for anal furunculosis awaits further study.