Background/aims-Uveal melanoma is the commonest malignancy of the eye, with a high proportion of patients dying of metastatic disease. Tumours showing a loss of chromosome 3 and gains of chromosome 8 are associated with a worse prognosis. The eYciency of fluorescence in situ hybridisation (FISH) in determining copy numbers of these chromosomes was assessed in individual tumours and related to patient survival. Methods-33 fresh frozen samples were analysed with centromeric probes for chromosomes 3 and 8. Patient outcomes were divided into two groups: (1) absence of genetic abnormalities (no genetic imbalance) and (2) presence of genetic abnormalities (genetic imbalance). The log rank test was used to compare survival, which was represented by KaplanMeier survival curves. Results-Of the 33 tumours analysed, 16showed evidence of genetic imbalances. Of these 16 tumours, 14 patients had died by the end of the study, with 10 having died of liver metastases. Of the tumours without evidence of genetic imbalances, five patients had died by the end of the study, although none had died as a result of either liver metastases or from the primary uveal melanoma. The diVerence in survival between the two groups was highly significant (p<0.0001). Conclusion-The authors have shown that FISH analysis for chromosome 3 and 8 is a reliable and eYcient technique in the analysis of fresh frozen tumour specimens and is valuable in the prediction of prognosis in individuals with uveal melanomas.