The efficacy of cyclosporin A (CsA) for the treatment of canine atopic dermatitis was evaluated based on the systematic review of prospective clinical trials published between 2001 and 2005. Ten studies with adequate design characteristics were included. These studies enrolled 799 dogs, 672 (84%) treated with CsA, 160 (20%) with placebo, 74 (9%) with oral glucocorticoids and 23 (3%) with antihistamines. Treatment duration varied from 2 weeks to 6 months. For safety analysis, data were available from 660 dogs. Lesion scores were improved from baseline in the range of 30-52%, 53-84% and 52-69% after 4, 6 and 16 weeks, respectively. The percentage of dogs with only mild pruritus rose from 0-13% at inclusion to 32-59% and 46-90% after 4 and 12 weeks, respectively. In most studies, the frequency of CsA administration could be reduced to every other day in 40% to 50% of patients after 4 weeks and to twice weekly in 20-26% of the dogs after 12-16 weeks. Meta-analysis confirmed highly significant effects of CsA compared to placebo, but none between oral CsA and glucocorticoids. The initial disease severity, age or body weight of subjects did not influence treatment success. Improvement by more than 50% over baseline of lesion scores was predictive of a better response during treatment maintenance. Vomiting and soft stools/diarrhoea were the most frequent adverse events seen at least once during the studies. These occurred in 25% and 15% of subjects, respectively. The frequency of each other type of adverse events was lower than 2.1%. In summary, the administration of CsA for the treatment of canine AD was found to be as effective as that of glucocorticoids, and adverse effects were minimal.