BACKGROUND: Adapalene is a new synthetic retinoid analogue developed for the topical treatment of acne vulgaris. OBJECTIVE: The study was designed to compare the efficacy and safety and adapalene gel 0.1% with tretinoin gel 0.025% in the treatment of grade II to II facial acne vulgaris. METHODS: Three hundred twenty-three patients were enrolled in this investigator-masked, randomized, parallel group, multicenter trial. Patients applied the test materials to the entire facial area daily, for a period of 12 weeks. Efficacy and cutaneous tolerance were assessed at baseline and weeks 2,4,8, and 12. Efficacy was determined by investigator counts of noninflammatory open and closed comedones, and inflammatory papules and pustules, as well as global improvement. Cutaneous tolerance was evaluated by erythema, scaling, and dryness, along with burning and pruritus. RESULTS: Staring at weeks 2 and 4, adapalene gel produced numerically greater lesion reductions than did tretinoin gel for all lesion types. At week 12, the mean percent reduction in the different lesion counts was as follow: 49% versus 37% for total lesions (p<0.01); 46% versus 33% for noninflammatory lesions (p=0.02); 48% versus 38% for inflammatory lesions (p=0.06) in adapalene and tretinoin gel treatment groups, respectively. Cutaneous side effects were limited to a mild "retinoid dermatitis" occurring in both treatment groups; however, patients treated with adapalene gel tolerated this therapy significantly better than those treated with tretinoin gel. Laboratory test evaluations (hematology, blood chemistries, urinalysis) were performed in 54 patients before and after 3 months of treatment. No clinically significant changes were observed. CONCLUSION: Adapalene gel 0.1% applied once daily was significantly more effective in reducing acne lesions and was better tolerated than tretinoin gel 0.025% in the treatment of acne vulgaris.