A randomized, double-blind, placebo-controlled phase III clinical trial was performed to assess megestrol acetate (Megace) as a postsurgical adjuvant therapy for patients with locally advanced malignant melanoma. Patients whose tumors were greater than 1.7 mm thick and had no regional lymph node involvement and patients with regional lymph node involvement were randomized to receive either 160 mg twice per day oral suspension of megestrol acetate or placebo. Treatment was administered for a maximum of 2 years or until disease progression. The study accrued 262 eligible patients. All but two patients were followed until death or a minimum of 4.5 years. Disease progression was documented in 156 patients. Neither progression-free survival (PFS) nor overall survival (OS) was found to differ between the treatments. The median PFS was 2.4 years in the megestrol acetate arm and 2.3 years in the placebo arm. Multivariate analysis revealed a significantly decreased PFS for patients with four or more positive regional lymph nodes and metachronous nodal disease. Median OS was 5.3 years in the megestrol acetate arm and 3.9 years in the placebo arm. Multivariate analysis revealed that OS was significantly decreased for patients 70 years of age or older with four or more positive lymph nodes. Adjuvant therapy with megestrol acetate oral suspension administered at a dose of 160 mg twice a day for 2 years was not found to be effective in prolonging PFS or OS in patients with surgically resected, locally advanced melanoma.