Background Adult patients with atopic dermatitis (AD), especially with the head-neck distribution, are often sensitized to the lipophilic yeast Malassezia furfur/Pityrosporum orbiculare, which is considered to contribute to the pathogenesis of the dermatitis. Objective Evaluation of the efficacy of oral ketoconazole on immunological and clinical parameters in yeast allergic adult patients with AD. Study design Randomized double-blind placebo-controlled study. Subjects Twenty-nine patients with specific IgE antibodies to M. furfur/P. orbiculare and with elevated serum IgE participated in the investigation. Fifteen subjects were treated with 200 mg, ketoconazole daily and 14 received placebo for 3 months. Betamethasone cream was allowed as supplementary therapy and the consumption was registered. The clinical score (SCORAD), total serum IgE and specific IgE antibodies to M. furfur/P. orbiculare, Candida albicans and Dermatophagoides pteronyssinus were monitored at the starting point and by the end of the first and third month. Results In the actively treated group the levels of specific IgE to M. furfur/P. orbiculare and C. albicans as well as total serum IgE decreased significantly. Sensitization to D. pteronyssinus was not influenced. The clinical score decreased in both groups, and the improvement was correlated to the consumption of topical steroids in the control group but not in the ketoconazole group.