20% azelaic acid cream was compared clinically with it vehicle in a 3-month double-blind study of 92 patients with moderate inflammatory acne. In a single-blind study of 289 patients with comedonal acne, the topical azelaic acid preparation was compared with 0.05% tretinoin cream over a period of 6 months. In both controlled studies, 20% azelaic acid cream significantly reduced the number of acne lesions and yielded clinically relevant improvement rates. Azelaic acid cream was significantly and substantially more effective than its vehicle, indicating that the dicarboxylic acid itself is an active drug in acne treatment. In the study of comedonal acne, 20% azelaic acid cream was equally effective as 0.05% tretinoin cream in reducing the number of comedones and with respect to overall response. However, azelaic acid cream was better tolerated, causing fewer local side effects than the topical retinoid.