Studies of gender differences in colorectal cancer have shown temporal shifts in incidence and site distribution which can be attributed, in part, to environmental and behavioural factors. In high-risk populations, rectal cancer and left-sided colon cancer have been more frequent in older men, whereas right-sided colon cancer has been more commonly found in older women. Among known associations with reduced colorectal cancer risk, women appear to ingest more dietary fibre, seem to benefit more from physical activity and body mass, and consume less alcohol. Although these differences may contribute to the risk differential, hormonal events during reproductive years also appear to affect women's risk at older age. The interactions of sex hormone metabolism and nutrition, including dietary fibre, in colorectal carcinogenesis provide a rewarding field for investigation.