The clinical records of 277 cases of canine atopy treated with specific allergen immunotherapy were reviewed. A good response was defined as control with immunotherapy either alone or with topical agents, a partial response as control with immunotherapy and other systemic agents, and a poor response as no perceived benefit and the immunotherapy discontinued. The mean follow-up period was 29.2 months (range 10 to 85 months). Ninety-one cases (33 per cent) were lost to follow-up or failed to comply with the therapeutic protocol. Of the remaining 186 cases, 40 (21.5 per cent) had a good response to immunotherapy, 74 (39.8 per cent) had a partial response, and 72 (38.7 per cent) had a poor response. Immunotherapy was therefore of long-term benefit in 114 dogs (61.3 per cent). No significant differences in response rates were associated with the breed or sex of the dog, or the age of onset of the disease, or with the type or number of allergens included in a vaccine. Dogs which had clinical signs for more than 61 months before immunotherapy had a significantly poorer response rate (23.5 per cent, P < 0.05). In-house cases had a significantly better response rate (95.2 per cent, P < 0.05) than externally managed cases.