Among the population of Reggio Emilia, Italy, 56 patients with polymyalgia rheumatica (PR) and giant cell arteritis (GCA) were identified during the 5-year period 1981-85. The average annual incidence rates of PR and GCA were 12.8 and 8.8 respectively per 100,000 population aged 50 years or older. Forty-nine patients were followed up and the mean duration of follow-up was 32 months. All the patients received steroid therapy. We have evaluated the cumulative probability of requiring continued steroid therapy between patients with PR only, GCA only, and PR associated with GCA using life-table methods with permanent discontinuation of therapy as an end point. The different duration of steroid therapy between these 3 groups did not achieve statistical significance by the method of Lee and Desu. We identified a 5 variable discriminant function that correctly predicted whether the duration of therapy would be longer or shorter than 16 months (median duration of therapy) in 80% of our patients followed up for at least 24 months. The presence of synovitis in PR is also discussed.