Activation of CDK4 by amplification, increased expression of Cyclin D1 (CCND1) or reduced expression of the CDK inhibitor p16 (CDKN2A) can contribute to transformation of melanocytes indicating that CDK4 can act as an oncogene in melanoma. To explore if CDK4 may be a viable target for the treatment of human melanoma we screened a panel of melanoma cells with a highly selective CDK4/6 inhibitor PD-0332991 (PD-991). To explore possible genomic predictors of sensitivity we also performed gene expression profiling and mutation analysis on these cells. The majority of melanoma cells were sensitive to PD-991, however there was a distinct resistant group. Low CDKN2A mRNA expression or mutation or loss of CDKN2A predicted sensitivity to PD-991 (p<0.02), and this was confirmed at the level of p16 protein expression. Loss of RB protein correlated with resistance. In addition, mutated p53 and low MDM2 and p21 gene expression (p53 transcriptional activity) was a strong predictor of PD-991 resistance (p<0.0001). Expression of CDK4, CCND1 or other cyclins or CDK-inhibitors did not predict sensitivity to PD-991. Sensitive melanoma cell lines treated with PD-991 show a decrease in hyperphosphorylated RB and a concomitant G0/G1 cell cycle arrest and senescent phenotype. Taken together these data support evaluation of CDK4 inhibitors in melanoma and suggest that CDKN2A may be a genomic predictor of sensitivity whereas p53 mutation a marker of resistance.