Within the Danish ‘Diet, Cancer and Health’ cohort, we aimed to investigate the association between prediagnostic fish intake (total, lean, fatty) and (a) incidence of total and high-grade prostate cancer and (b) the risk of all-cause and prostate cancer-specific mortality among men with prostate cancer. Among 27 178 men, 1690 prostate cancer cases were identified through 2012. Of these, 1042 had a Gleason score of 7 or above and 498 had a Gleason score of 8 or above at the time of diagnosis; 364 died (n=228 from prostate cancer) during follow-up through 2013. Cox proportional hazard models were used for the statistical analyses. No association between any type of fish intake and risk of total prostate cancer or high-grade prostate cancer (Gleason score≥7 or ≥8) was found. For all-cause mortality, we found no association for any type of fish intake. For prostate cancer-specific mortality, only a higher intake of fatty fish was associated with a higher mortality [per daily 25 g increment in intake (mortality rate ratio=1.27; 95% confidence interval: 1.04–1.55; P=0.02)]. In conclusion, no strong association was found between fish consumption and the risk of or mortality from prostate cancer. Only a higher intake of fatty fish was associated with a higher risk of prostate cancer-specific mortality.