['To investigate the relation between patient survival and incrementally increasing percentages of fluorescence in situ hybridization-determined complete loss of chromosome 3 (monosomy 3) and gain of chromosome 8q in primary uveal melanoma cells.', 'Clinicopathological factors were related to disease-free survival. Fluorescence in situ hybridization was performed using probes on chromosomes 1, 3, 6, and 8. The percentages of UM cells with monosomy 3 or chromosome 8q gain were classified in groups with incrementally increasing percentages and related to disease-free survival. Correlations between clinical factors and cytogenetic aberrations were also analyzed.', 'Two-hundred twenty choroidal and ciliary body melanomas were analyzed. The following proved to be significant predictors of survival in univariate analysis: older patient age (P = 0.003); large tumor diameter (P < 0.001); mixed cell type (P = 0.001); presence of closed microvascular loops (P < 0.001); loss of chromosome 1p (P = 0.006); monosomy 3 (P < 0.001); gain of 6p (P < 0.001); and gain of chromosome 8q (P < 0.001). Multivariate Cox analysis displayed monosomy 3 (Hazard ratio [HR] 2.83, P = 0.002) and gain of chromosome 8q (HR 3.13, P = 0.002) as the most important independent prognostic factors of poor survival, followed by older patient age (HR 1.02, P = 0.017). Increasing percentages of monosomy 3 and gain of chromosome 8q in tumor cells showed a correlation with worse prognosis (Log-rank test 49.9 and 40.4, both P < 0.001) and increased number of additional copies of 8q correlated with shorter disease-free interval (Log-rank test 45.7, P < 0.001).'] Do higher percentage of FISH-determined monosomy 3 and 8q amplification in uveal melanoma cells relate to poor patient prognosis?