The gene of the cyclin-dependent kinase 4 (CDK4)-inhibitor p16INK4A (CDKN2/MTS1) has been proposed as a candidate for a tumor-suppressor gene located on chromosome 9p21, a frequently deleted region in a series of human cancers including malignant melanoma. An increasing and sometimes conflicting body of data has accumulated regarding the frequency of homozygous deletions and mutations as well as the importance of p16INK4A in malignant melanoma. The purpose of this review is therefore to summarize the current knowledge on p16INK4A and to discuss its biologic significance in the pathogenesis of melanocytic tumors.