It has been suggested that components of our diet play an essential role in carcinogenesis. Anthropometric indices, such as body weight and height, have often been considered as measurements of prevailing diet and nutrition in childhood respectively. To investigate to what extent height and body weight are associated with the risk of gastrointestinal cancer, data from a Norwegian screening programme for tuberculosis were analysed. More than 1,100,000 individuals, aged 30-69 years at the time of examination, were included in the study. Body weight, expressed as Quetelet's index (QI), and height records were linked with vital status data from Statistics Norway and the Cancer Registry of Norway. The analysis shows that individuals in the first quintile of height had a lower relative risk than later quintiles for colon cancer, independent of sex and stage of disease at completion of follow-up. The association between height and rectal cancer is similar, but weaker. Men in the fifth quintile of QI have a relative risk of 1.39 for colon cancer, compared with the first quintile, and they also have a slightly elevated risk for rectal cancer. Among women, the pattern is unclear, but we observed a significant relationship between high QI and cancer of the gallbladder. Our results indicate that prevailing diet and living conditions in early life do play a role, and seem to support the hypothesis that anthropometric indices could be of importance as indirect markers for the risk of colon cancer and, to some extent, for cancer of the rectum and gallbladder.