Lynch syndrome (LS) is one of the inherited colorectal cancer (CRC) syndromes and is due to germline mutations in one of the mismatch repair (MMR) genes. Within LS affected-families the expression of the syndrome varies, which suggests that other factors, such as lifestyle factors, have an influence on the LS phenotype. This review gives an overview of studies that assessed the role of lifestyle factors in the development of CRC in LS. Several published studies investigated smoking habits or body fatness (BMI) in relation to colorectal tumours. Those studies fairly consistently suggest that smoking and a high BMI markedly increase the risk of CRC in persons with LS. Other lifestyle factors, such as physical activity, alcohol or diet have not or only scarcely been studied. Lifestyle factors may indeed affect CRC risk in LS. However, more prospective studies with only confirmed MMR gene mutation carriers should be done to further elucidate the role of all lifestyle factors in CRC and in other types of cancer in persons with LS. Information on the role of lifestyle factors in the development of LS-associated cancers may help in establishing lifestyle and dietary recommendations with the ultimate goal of decreasing cancer risk in persons with LS.