OBJECTIVE The aim of the study was evaluation of genetic changes: loss of heterozygosity (LOH) and microsatellite instability (MSI) in the genome of cells of the uveal melanoma. METHODS The incidence of MSI and LOH in cells of uveal melanomas was examined in tissue specimens obtained at surgical resection of the tumour in 14 patients. The results were related to respective MSI and LOH incidence in the genome of peripheral blood cells of the same patients. DNA was isolated with organic extraction. The fluorescent multiplex polymerase chain reaction (PCR) was used to amplify microsatellite loci included in commercially available human identification kits. Phenotyping was performed with the use of ABI Prism 310 Genetic Analyzer. RESULTS MSI and LOH was found in 6 of 14 cases of uveal melanoma, manifested at one or more loci. MSI was present in chromosomes 3, 11 and 16. LOH was detected in chromosomes: 2, 3, 8, 13, 16 and 19. Genetic instability of the LOH/MSI type was detected in 3 patients with long anamnesis and large tumor infiltrating retrobulbar structures (pT4 feature). Two patients died within a year because of generalized cancer disease. CONCLUSIONS 1 Loss of heterozygosity and microsatellite instability is present in uveal melanomas. 2. Genetic instability of LOH/MSI type associates with advanced size of tumour and progression of neoplastic disease.