Low sunlight exposure confers increased prostate cancer risk. In a study conducted in northern England, we investigated how combinations of exposure measures affect this risk. Recursive partitioning was used to identify combinations of exposure parameters that distinguished 453 prostate cancers from 312 benign hypertrophy patients. Sunbathing score most significantly defined cancer patients; 78.7% men with low scores (</=3.0) and 40.2% men with high scores (>8.0) had cancer. These subgroups were stratified by childhood sunburning, holidays in a hot climate and skin type such that subgroups with a 13.0-fold increased risk of cancer were identified.