Loss of heterozygosity (LOH) of selected regions at chromosomes 3p and 17p in non-small cell lung cancer (NSCLC) and the association of these abnormalities with major clinical parameters and prognosis were studied.The study group included 92 consecutive primary NSCLC tumours and four microsatellite markers from chromosome 3p and three markers from 17p were analyzed.LOH of at least one locus was found in 83% of all analyzed tumours. Most frequently deletion (58%) was found at locus D3S1481 (3p14.2). Sequence deletions of D17S520 (17p12) and TP53 (17p13.1) occurred in 52% of tumours. LOH occurrence at 3p and 17p was more frequent in squamous cell carcinomas compared to adenocarcinomas (89% vs. 75%), but this difference was not significant.No significant association was found between LOH on any analyzed loci and tumour stage (TNM) and grade (G). There was no correlation between LOH and survival.