Dietary pattern analyses have increased the possibilities to detect associations between diet and disease. However, studies on dietary pattern and prostate cancer are scarce. Food intake data in the Uppsala Longitudinal Study of Adult Men cohort was determined by 7-day food records. Adherence to a modified Mediterranean Diet Score (mMDS) and a low carbohydrate-high protein (LCHP) score were grouped as low, medium, or high in the whole study population (n = 1,044) and in those identified as adequate reporters of energy intake (n = 566), respectively. Prostate cancer risk was analyzed with Cox proportional hazard regression (median follow-up 13 years) and competing risk of death was considered. There were no associations between dietary patterns and prostate cancer (n = 133) in the whole study population. Among adequate reporters the mMDS was not associated with prostate cancer (n = 72). The LCHP score was inversely related to prostate cancer in adequate reporters, adjusted hazard ratios; 0.55 (0.32-0.96) for medium and 0.47 (0.21-1.04) for high compared to low adherent participants (P-for-trend 0.04). Risk relations were not attributable to competing risk of death. In this study, a LCHP diet was associated with lower prostate cancer incidence. Relations emerged in adequate reporters, underscoring the importance of high-quality dietary data.