The influence of growth hormone and insulin-like growth factor I on human melanocytes is being increasingly recognized. Clinical evidence has shown that when recombinant human growth hormone (hGH) is administered to children of short stature, the growth of melanocytic naevi is boosted. This study was conducted on 56 hGH-triggered naevi and nine similar lesions excised before or after hGH therapy for hypopituitarism and Turner's syndrome. A series of 40 naevi excised from age-matched healthy children served as controls. Atypicality of naevocytes was investigated using image analysis, AgNOR counts, immunohistochemistry (HMB-45, NKI-C3, Ki-67, anti-bcl-2-oncoprotein), and DNA flow cytometry. The data associate hGH treatment with anisokaryosis and increased AgNOR and Ki-67 counts in naevocytes. The same cells also show abnormal patterns of HMB-45 immunolabelling. These indications of naevocyte activation were not suggestive of malignant transformation. hGH-triggered melanocytomas should be added to the list of atypical melanocytic naevi. The long-term evolution of these lesions remains unknown and the potential risk of malignant transformation awaits careful evaluation.