In this study we assessed the expression of the Melan-A/MART-1 antigen by immunohistochemistry using monoclonal antibody A103 in 73 primary cutaneous melanomas and its correlation with tumor staging and patient survival. Melan-A/MART-1 was expressed in 90% of primary tumors, with loss of expression increasing with Breslow thickness. Kaplan-Meier analysis demonstrated a significantly reduced disease-free interval and overall survival rate for patients not expressing this antigen. The poor prognosis of such patients was even worse for those presenting with a primary melanoma and a Breslow thickness of > or = 1 mm. Thus, Melan-A/MART-1 is not only a useful and specific additional marker for the diagnosis of primary cutaneous melanoma, but it may also help refine the prognosis of patients with malignant melanoma.