We have undertaken a retrospective analysis of all positron emission tomography (PET) scans carried out at St Thomas’ Hospital, London, since 1994 to establish the sensitivity and specificity of this radiologic technique in cutaneous malignant melanoma. In particular, we have identified those patients with primary cutaneous malignant melanoma in whom PET scanning revealed in-transit or regional spread to nodes and those patients with known regional spread in whom PET scanning revealed distant metastases. We defined our false-negative results as a negative scan result with positive histology or subsequent clinical progression of disease. False-positive results were defined as a suspect scan with negative histology or no subsequent progression of disease. PET scanning had an overall sensitivity of 78% and specificity of 87%; however, subset analysis (M. D. Anderson staging system) showed a sensitivity of 50% for stage I disease (34 patients and 35 scans) and 33% for stage II disease (9 patients and 9 scans) with specificities of 87% and 100%, respectively. For stage III disease (16 patients and 17 scans), PET showed a sensitivity of 93% and specificity of 50%. Overall, 35% of patients with true-positive scans had their disease restaged. We can conclude therefore that PET is valuable as a staging procedure in patients with known regional spread but is suboptimal in the prediction of outcome in stage I or stage II disease. (J Am Acad Dermatol 2000;42:606-11.)