Cytogenetic analysis of 28 cases of non-small cell lung cancer (NSCLC) was carried out in an attempt to determine karyotype changes involved in the early state of disease. Our findings indicate that, even though karyotypes are very complex, recurrent cytogenetic changes can be identified. The most common structural rearrangements were deletions of chromosomes 3, 17 and 9. The most frequent numerical alterations were gain of chromosomes 7 and 20 and loss of chromosomes 1 and Y. In particular, the high frequency of deletions suggests a critical role of suppressor oncogenes in these chromosome regions in tumor development.