BACKGROUND: Recent studies have shown that some four in ten cancers are attributable to a few key risk factors. The aim of this study was to estimate cohort-based population attributable fractions (PAFs) in Finland for potentially modifiable cancer risk factors. METHODS: Data from eight health studies including 253,953 subjects with 29,802 incident malignant solid tumors were analysed using Bayesian multivariate regression model with multiplicative risk factor effects. We estimated the effects of smoking, excess body weight, alcohol consumption, physical activity, parity and education on cancer incidence and related PAFs by cancer site, accounting for competing mortality. RESULTS: PAF for all cancer sites and exposures combined was 34% (95% credible interval 29%-39%) in men and 24% (19%-28%) in women. In men, 23% (21%-27%) and in women 8% (6%-9%) of all cancers were attributed to smoking. PAF related to excess body weight was 4% (2%-6%) in men and 5% (2%-7%) in women, to alcohol 7% (3%-10%) in men and 4% (0%-7%) in women, and to excess body weight and alcohol combined 10% (6%-15%) in men and 9% (4%-13%) in women. CONCLUSION: Smoking was the most important factor contributing to cancer burden in Finnish men and women over the last 40 years. The contribution of excess body weight and alcohol consumption together outweighed the role of smoking in women. As the prevalence of overweight is expected to increase, more efficient public health measures supporting adherence to healthy weight are essential to reduce cancer burden.