Objective. —To learn about the natural history of untreated, early-stage prostatic cancer. Design. —Cohort study with a mean follow-up of 123 months (range, 81 to 165 months). Setting. —Population-based, regionally well defined. Patients. —A consecutive sample of 223 patients (98% of all eligible) with earlystage (T0-2, NX, MO), initially untreated prostatic cancer. Main Outcome Measures. —Progression-free, disease-specific, and overall survival. Need for palliative and terminal care. Intervention. —Patients with tumor progression were hormonally treated (orchiectomy or estrogens) if they had symptoms. Results. —After complete follow-up, only 19 (8.5%) of the 223 patients had died of prostate cancer and 105 (85%) of a total of 124 deaths were from other causes. The 10-year, disease-specific survival rate was 86.8% (95% confidence interval, 80.7% to 92.9%) and was equally high (87.9%) in a subgroup of 58 patients who met current indications for radical prostatectomy. The progression-free, 10-year survival rate was 53.1% (95% confidence interval, 44.2% to 62.0%). In 50 of 76 patients, local growth provided the only evidence of progression, and endocrine treatment was generally successful in these cases. Following an initial increase, the rate of disease progression and death from prostate cancer decreased during the last years of follow-up. Conclusion. —The low disease-specific mortality rate, especially in patients with highly and moderately differentiated tumors, means that any local or systemic therapy intended for patients with early prostatic cancer must be evaluated in clinical trials with untreated controls for comparison. (JAMA. 1992;267:2191-2196)