In designing national strategies for genetic testing, it is important to define the full spectrum of pathogenic mutations in prostate cancer (PCa) susceptibility genes. To investigate the frequency of mutations in PCa susceptibility genes in Polish familial PCa cases and to estimate gene‐related PCa risks and probability of aggressive disease, we analyzed the coding regions of 14 genes by exome sequencing in 390 men with familial prostate cancer and 308 cancer‐free controls. We compared the mutation frequencies between PCa cases and controls. We also compared clinical characteristics of prostate cancers between mutation carriers and noncarriers. Of the 390 PCa cases, 76 men (19.5%) carried a mutation in BRCA1, BRCA2, NBN, ATM, CHEK2, HOXB13, MSH2 or MSH6 genes. No mutations were found in BRIP1, PTEN, TP53, MLH1, PMS2 and SPOP. Significant associations with familial PCa risk were observed for CHEK2, NBN, ATM, and HOXB13. High‐grade (Gleason 8‐10) tumors were seen in 56% of BRCA2, NBN or ATM carriers, compared to 21% of patients who tested negative for mutations in these genes (OR = 4.7, 95% CI 2.0‐10.7, P = .0003). In summary, approximately 20% of familial prostate cancer cases in Poland can be attributed to mutations in eight susceptibility genes. Carriers of mutations in BRCA2, NBN and ATM develop aggressive disease and may benefit from intensified screening and/or chemotherapy. What's new? Genetic susceptibility plays an important role in prostate cancer (PCa). In designing genetic‐testing strategies for PCa screening, it is important to define the full spectrum of pathogenic mutations that increase PCa risk. In this study, the authors found that approximately 20% of familial prostate cancer cases in Poland can be attributed to mutations in eight susceptibility genes. In addition, carriers of mutations in BRCA2, NBN and ATM are more likely to develop aggressive disease. These patients may benefit from intensified screening and/or chemotherapy.