An extensive retrospective survey of patients with onset of symptoms of nonspecific protocolitis arising in the decade 1967-1976 was carried out in northeastern Scotland, including the Grampian region, Orkney, and Shetland. Five hundred and thirty-seven cases were identified, and a 97% follow-up was achieved. One hundred and twenty nonhospitalized cases were included. The average annual incidence was 11.3 per 10(5) population, the highest recorded in Europe to date. Moreover, a striking rise in the incidence was noted. A bimodal age distribution and urban predominance was found. The frequency of both nonspecific proctocolitis and Crohn's disease in first-degree relatives was high. The disease was found to be less severe and extensive at onset than suggested by other surveys, 70% having only distal involvement and 68% having a mild first attack. The overall mortality and surgical resection rates in the first attack were both 3%. Severe first attacks carried a striking 23% mortality. The observed long-term mortality differed little from the expected, except in patients with extensive disease or severe first attacks, or both. The risk of relapse correlated with decreasing age at onset but not with the initial extent or severity of disease. The surgical resection rate after 5 yr was 8%. Twelve percent of patients extended their disease by 5 yr. Using the patient-year concept, 68% of patient years were remission years. The youngest age group had the highest percentage of attack years. The percentage of attack years for all patients correlated more closely with extent of disease in each patient year rather than extent of disease at diagnosis.