A primary duodenal adenocarcinoma, a tumor type for which no previous chromosome data existed, was cytogenetically analyzed after short-term culture. The main tumor mass was localized in the pancreatic head, but the histopathologic examination revealed its duodenal origin. A total of six abnormal, karyotypically unrelated, clones were identified. The largest exhibited clonal evolution and consisted of two subclones with massively rearranged karyotypes in the hypodiploid and hypotetraploid range. Chromosome imbalances brought about by these complex changes were gain of 1q, losses of chromosomes 6 and 9, and total or partial losses of 1p, 3p, 3q, 9p, 10p, 17p, 17q, 18q, 20p, and 20q. The remaining five smaller clones had 1-2 numerical or balanced structural chromosome aberrations. The present study thus revealed yet another epithelial tumor type characterized by karyotypically unrelated clones. For this as for other tumors, the pathogenetic significance of such cytogenetic polyclonality remains uncertain.