Cyclin D1 (CCND1, PRAD1, bcl-1) is associated with progression through G1 and entry into S phase of the cell cycle, as a partner of cyclin-dependent kinases (CDKs). The aim of this study was to evaluate cytogenetic aberrations of the gene locus at chromosome 11q13 in cutaneous malignant melanoma. Fluorescence in situ hybridisation (FISH) was applied on metaphase spreads of short-term primary cell cultures as well as on 5 microm paraffin tissue sections of primary melanomas and melanoma metastases, and on melanoma cell lines (C32, WM 266-4, HT 144, RPMI 7951, SK MEL 28). For FISH analysis DNA probes specific for Cyclin D1, centromere 11 and painting probes for whole chromosome 11 were used. FISH revealed additional Cyclin D1 gene copies in relation to centromere 11 copy numbers in 9/19 (47%) primary melanomas and in 7/20 (35%) melanoma metastases. The melanoma cell line SK MEL 28 also showed extra Cyclin D1 gene copies. A 24-colour FISH (mFISH) investigation revealed translocated chromosome 11 material to chromosomes 12, 14, 15, 20, 21, 22 and Y in these cases, respectively. Positivity for Cyclin D1 protein was detected by immunostaining in 17/19 (89%) primary melanomas (10 weak, 7 strong expression) and in 9/12 (75%) melanoma metastases (5 weak and 4 strong). All primary melanomas and 3/4 examined metastases with additional Cyclin D1 gene copies concomitantly revealed positive protein staining. Based on these results Cyclin D1 could well be involved in the pathogenesis of a subset of malignant melanoma. Additional studies will have to elucidate the role of further genes located at chromosome 11q13.