Background Some studies suggest that raised blood pressure may increase prostate cancer risk. We investigated associations of blood pressure with prostate cancer within the CONOR collaborative cohorts of Norway. Methods Between 1994 and 2003, 82,098 men from ten population-based cohorts in Norway completed standardised questionnaires and physical examinations, including resting blood pressure. The unique 11-digit identification number of Norwegian citizens allowed linkage with the Cancer Registry of Norway. Results A total of 78,768 (96%) men who were cancer-free at baseline and average age of 50.3 years (standard deviation, SD: 15.2) were followed up for a mean of 9.15 years. 11.4% of these men used antihypertensive drugs at baseline. During follow-up (1994–2006), 1,974 incident prostate cancers were diagnosed. We found a 4% (95% confidence interval, CI = 0–9%) increased risk of prostate cancer per one SD (18.3 mmHg) increase in systolic blood pressure and similar findings for diastolic blood pressure (hazard ratio, HR: 1.05 per SD; 95% CI = 1.01–1.10). The association was stronger for advanced (HR: 1.16 per SD increase in systolic blood pressure; 95% CI = 1.05–1.27) compared with localised (1.01; 0.95–1.08) prostate cancer (p for heterogeneity in hazard ratios = 0.02). Conclusions Raised blood pressure was associated with an increased risk of prostate cancer, particularly advanced cancers at diagnosis. Understanding the mechanisms underlying these findings may provide biological insights into prostate carcinogenesis. Even if the association was causal, our data suggest that raised blood pressure would account for only 3% of prostate cancers, so the public health impact of this association may be limited.