We described a 15-year-old boy with Gardner syndrome (GS), mental retardation, and craniofacial abnormalities. High-resolution banding analysis showed an interstitial deletion of the long arm of chromosome 5 (q22.1----q31.1). The breakpoints in the present case and in 3 previously reported 5q- patients with adenomatous polyposis coli suggest that the gene responsible for GS/or familial polyposis coli (FPC) is in the 5q22 region, a result consistent with the findings of linkage studies.