OBJECTIVES: To study the long-term survival of patients with prostate cancer, determine the risk factors for prostate cancer death, and investigate the outcome of initially untreated localized prostate cancer and incidentally detected tumors. METHODS: The survival of 813 patients in a population-based cohort of patients with prostate cancer in Linköping, Sweden, diagnosed from 1974 to 1986, was analyzed. RESULTS: At 10, 15, and 20 years after diagnosis, the prostate cancer-specific survival rate of men with localized, initially untreated, prostate cancer was 85.0% (95% confidence interval [CI], 79.0% to 91.0%), 80.0% (95% CI, 72.5% to 87.5%), and 62.6% (95% CI, 43.0% to 82.2%). Age 70 years or older, advanced stage, and poor differentiation were risk factors associated with an increased risk of prostate cancer death. At 10 years, the prostate cancer-specific survival rate among men with localized tumors treated by expectancy was 90% (95% CI, 84% to 97%) for grade 1 tumors, 74% (95% CI, 60% to 89%) for grade 2 tumors, and 59% (95% CI, 29% to 90%) for grade 3 tumors. For patients with incidentally detected tumors, the grade of malignancy was a more important risk factor than tumor volume. CONCLUSIONS: Patients with localized tumors have a favorable prognosis, even without initial treatment. However, when deciding on therapy, the grade of malignancy should be taken into account, as it has a great influence on survival. We did not see a tendency toward increased mortality when the patients were followed up for longer than 10 years after diagnosis.