This paper reviews the literature on colorectal cancer from a sex and gender-based perspective. Colorectal cancer is a major cause of death in the developed world, with rates increasing in developing countries. Although described by some writers as an 'equal opportunity' disease, it presents more risk to men than women. Both biological, or sex-linked factors, and gender-linked factors play a part in the aetiology of the disease, while gender differences in the use of screening and treatment also help shape the mortality gap between women and men for this condition. Without an appreciation of the part played by sex and gender in the risk of colorectal cancer, and without a gender-sensitive approach to screening in particular, it is possible that the mortality gap between men and women for this condition will widen in the future. ß 2007 WPMH GmbH. Published by Elsevier Ireland Ltd.There is an increasingly sophisticated understanding in medical science of the parts played by sex and gender in shaping the health of men and women, with an emerging specialism of gender medicine, alongside greater recognition of the need for gender-sensitive research and health care. However, gender is more commonly taken into account in areas of health where differences between women and men are particularly marked, for example in relation to specific conditions such as coronary heart disease, or health behaviours such as smoking. It is important to extend this debate to conditions where the differences between women and men appear to be less notable. Men and women largely die of the same conditions: worldwide around 27% of males and 32% of females die from cardiovascular disease, around 19% of both males and females die from infectious and parasitic diseases and 13% of men compared with 12% of women die from cancer [1]. While one difference between women and men that explains the gap in life expectancy is that women suffer many of the same health risks as men but at a later point in their life course, it is also important to consider the sex and gender differences influencing women's and men's risk of specific conditions such as cancer.This paper adopts a multi-disciplinary approach to explore sex and gender differences in the risk of colorectal cancer and in the role of screening to detect and treat early symptoms of the disease. The premise on which this paper is based is that an individual's risk profile for this disease is shaped by both biologically determined factors that influence vulnerability to the condition and gender or socially shaped factors that 1 Read the second part of this review in