Significance of tertiary Gleason pattern/grade 5 on prostatectomy has been studied, but its significance on biopsy remains uncertain. Recent International Society of Urological Pathology consensus conference recommended that biopsy Gleason score is generated by adding tertiary grade 5 to the primary grade. We examined the preoperative clinical and biopsy findings in 53 patients with biopsy tertiary pattern 5 and 119 patients with primary/secondary biopsy pattern 5. Prostatectomy findings and prostate-specific antigen (PSA) failure rates were compared in surgically treated patients. Cause-specific and all-cause mortality were compared in patients treated nonsurgically. At presentation, age, gland volume, PSA, and biopsy cancer volume were similar in patients with tertiary and primary/secondary grade 5. Only 20 patients underwent prostatectomy and 152 were treated nonsurgically. Regardless of the pattern, patients treated by prostatectomy were younger (P=0.003), had lower PSA (P=0.001), and less cancer on biopsy (P=0.0001). Prostatectomy findings and PSA failures were not significantly different in patients with tertiary grade 5 versus primary/secondary pattern 5. In nonsurgically treated patients, patients with primary pattern 5 compared with those with tertiary pattern 5 had a significantly higher risk of all-cause mortality [adjusted hazard ratio (HR): 2.33, 95% confidence interval (CI): 1.10-4.90, P=0.026] and cause-specific mortality (adjusted HR: 7.52, 95% CI: 2.84-19.87, P<0.001). In contrast, patients with secondary pattern 5 had a comparable all-cause mortality risk to patients with tertiary pattern 5 (adjusted HR: 1.04, 95% CI: 0.47-2.32, P=0.92), but had a marginally higher risk of cause-specific mortality than patients with tertiary pattern 5 (adjusted HR: 2.13, 95% CI: 0.75-6.10, P=0.16).