Objectives: To investigate the rate of prostate cancer-specific mortality (PCSM) and disease characteristics in patients diagnosed with localised prostate cancer at age 80–89 years in comparison with men diagnosed at age 70–79 years. Patients and Methods: This is a retrospective study of data from the South Australian Prostate Cancer Clinical Outcomes Collaborative (SA-PCCOC). Included were men diagnosed between 2005 and 2014, aged ≥70 years with no evidence of metastatic disease at presentation. Propensity score matching and competing risk Fine and Grey regression were used to assess the chance of treatment (curative vs non-curative) and treatment effect on PCSM. Results: Of the 1 951 eligible patients, 1 428 (76%) were aged 70–79 years and 460 (24%) were aged 80–89 years at diagnosis, with a median (interquartile range) age of 74 (72–76) and 83 (81–85) years, respectively. The 80–89 years group had higher Gleason scores and Prostate Specific Antigen (PSA) values (all P < 0.001) in comparison with the younger group. The 80–89 years group were less likely to be treated with curative treatment (odds ratio 0.12, 95% confidence interval 0.09–0.16; P < 0.001). The proportion of deaths attributable to prostate cancer was similar in both groups: 73 of 263 deaths (28%) in the 80–89 years group vs 97 of 310 deaths (31%) in the 70–79 years group. The risk of PCSM in individuals treated with curative intent was reduced in both groups. Conclusions: The proportion of prostate cancer deaths was similar in both groups. These findings support carefully selected individualised management of elderly patients diagnosed with localised prostate cancer.