We have investigated the familial aggregation of colorectal cancer and hereditary nonpolyposis colorectal cancer (HNPCC) in Egypt because of the high incidence of colorectal cancer in Egyptian children and young adults and the prevalence of consanguinity there. In a pilot study, we conducted detailed interviews with 111 Egyptian colorectal cancer patients and 111 healthy Egyptian controls about their family histories of colorectal cancer, and other cancers, consanguinity, age at diagnosis, symptoms and recurrence. Eight patients (7.2%) had one or more first- or second-degree relatives under age 40 with colorectal cancer, suggestive of HNPCC by the Amsterdam criteria. One of these families had a typical history of HNPCC, with 4 relatives having colorectal cancer in 3 generations; 3 of these relatives were younger than age 45 at colon cancer diagnosis, and other relatives had extracolonic tumors. Another 14 patients (12.6%) had a first- or second-degree relative with a family history of other neoplasms such as endometrial, urinary and hepatobiliary cancers that could also be related to HNPCC. Four patients with early-onset colon cancer and a family history of other HNPCC-related cancers reported that their parents were first-degree cousins.