We have investigated the potential for the p16-cyclin D-CDK4/6-retinoblastoma protein pathway to be exploited as a therapeutic target in melanoma. In a cohort of 143 patients with primary invasive melanoma, we used fluorescence in situ hybridization to detect gene copy number variations (CNVs) inCDK4, CCND1,andCDKN2Aand immunohistochemistry to determine protein expression. CNVs were common in melanoma, with gain ofCDK4orCCND1in 37 and 18% of cases, respectively, and hemizygous or homozygous loss ofCDKN2Ain 56%. Three-quarters of all patients demonstrated a CNV in at least one of the three genes. The combination ofCCND1gain with either a gain ofCDK4and/or loss ofCDKN2Awas associated with poorer melanoma-specific survival. In 47 melanoma cell lines homozygous loss, methylation or mutation ofCDKN2Agene or loss of protein (p16INK4A) predicted sensitivity to the CDK4/6 inhibitor PD0332991, while RB1 loss predicted resistance.