Cancer typically results in loosened control over genomic integrity, resulting in alterations of the genome of cancer cells. Comparative genomic hybridization (CGH) is a method that can be used on DNA extracted from routinely fixed tissue to assess the entire genome for the presence of changes in DNA copy number. CGH analysis has revealed that melanoma differs from melanocytic nevi by the presence of frequent chromosomal aberrations. In contrast, melanocytic nevi typically show no chromosomal aberrations, or have a restricted set of alterations with basically no overlap to melanoma. These marked differences between aberration patterns in melanomas and melanocytic nevi can be exploited diagnostically to classify melanocytic tumors that are ambiguous based on histopathologic assessment. In addition to potential diagnostic applications, detailed analyses of recurrent aberrations can lead to the identification of genes relevant in melanocytic neoplasia.