CONTEXT: UK Biobank is a prospective study of half a million subjects, almost all aged 40-69 years, identified in 22 centres across the UK during 2006-2010. OBJECTIVE: A healthy lifestyle has been described as 'better than any pill, and no side effects [5]. We therefore examined the relationships between healthy behaviours: low alcohol intake, non-smoking, healthy BMI, physical activity and a healthy diet, and the risk of all cancers, colon, breast and prostate cancers in a large dataset. METHOD: Data on lifestyle behaviours were provided by 343,150 subjects, and height and weight were measured at recruitment. 14,285 subjects were diagnosed with cancer during a median of 5.1 years of follow-up. RESULTS: Compared with subjects who followed none or a single healthy behaviour, a healthy lifestyle based on all five behaviours was associated with a reduction of about one-third in incident cancer (hazard ratio [HR] 0.68; 95% confidence intervals [CI] 0.63-0.74). Colorectal cancer was reduced in subjects following the five behaviours by about one-quarter (HR 0.75; 95% CI 0.58-0.97), and breast cancer by about one-third (HR 0.65; 95% CI 0.52-0.83). The association between a healthy lifestyle and prostate cancer suggested a significant increase in risk, but this can be attributed to bias consequent on inequalities in the uptake of the prostate specific antigen screening test. CONCLUSIONS: Taken together with reported reductions in diabetes, vascular disease and dementia, it is clearly important that every effort is taken to promote healthy lifestyles throughout the population, and it is pointed out that cancer and other screening clinics afford 'teachable moments' for the promotion of a healthy lifestyle.