High-resolution karyotypes were analyzed from lymphocyte cultures of 18 Norwegian polyposis patients, of whom two had classic Gardner syndrome (GS). We focused on possible rearrangements of the long arm of chromosome 5. Previously the gene for familial adenomatous polyposis (FAP) was localized to the region 5q21-22 by linkage analysis. A patient with a constitutional deletion in this region would be of great value in the course of cloning the gene. At the level of high-resolution G-banding, however, none of these patients showed any interstitial deletion or other rearrangement on chromosome 5 or any other chromosome.