In a population-based study, disease progression and survival were evaluated in untreated patients with newly diagnosed cancer of the prostate without distant metastases. Complete follow-up was achieved in 223 of 227 (98%) consecutively diagnosed, eligible patients of all ages. After 5 years, the cumulative progression-free survival (with 95% confidence interval) was 71.8 (65.5-78.1)% and survival corrected for causes of death other than prostatic cancer was 93.8 (88.3-97.6)%. Univariate and multivariate analyses showed no association between age at diagnosis and the natural course. Local progression was less common in localised, non-palpable tumours than in larger tumours. The rate of progression was 18.7 (6.1-57.1) times higher and that of disease-specific death 216.0 (31.2-1496) times higher in patients with poorly than in those with highly differentiated tumours. It is concluded that tumour grade at diagnosis is an excellent predictor of local and distant progression. The low death rate, especially in patients with highly and moderately differentiated tumours, 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.