Background: No consensus has been reached on the definite associations among prostatitis, benign prostatic hyperplasia (BPH) and prostate cancer (PCa). Hence, this meta-analysis was conducted to explore their triadic relation by summarizing epidemiological evidence. Methods: Systematical and comprehensive retrieval of online databases PubMed, PMC, EMBASE and Web of Science was performed to acquire eligible studies, up to April 1st, 2019. Pooled odds ratios (ORs) with 95% confidence intervals (CIs) were calculated to clarify their correlations. Results: A total of 42 studies were enrolled in the quality assessment and 35 were finally included in the meta-analyses. Among them, 27 studies were included to describe the association between prostatitis and PCa (OR=1.72, 95% CI=1.44-2.06, I(2) =90.1%, P<0.001). 21 studies presented significant evidence about the relation between BPH and PCa (OR=2.16, 95% CI=1.75-2.88, I²=97.1%, P<0.001). Due to the huge heterogeneity among studies, those with obvious outliers were excluded based on the Galbraith plots. Ultimately, 17 studies were screened out to assess the association between prostatitis and PCa (OR=1.59, 95% CI=1.48-1.70, I²=29.4%, P=0.123). Meanwhile, 8 studies were retained to evaluate the association between BPH and PCa (OR=3.10, 95% CI=2.87-3.35, I²=8.4%, P=0.365). As for the relation between prostatitis and BPH, a case-control study and a cohort study both supported that prostatitis could enhance the risk of BPH. Conclusions: Significant correlations were revealed among prostatitis, BPH and PCa. Prostatitis or BPH could lead to escalating risks of PCa. Meanwhile, people with a history of prostatitis might be more vulnerable to BPH.