This paper presents the results of an investigation made on the recent trends in the estimated prevalence and incidence rates of sarcoidosis in Japan and the changes in its epidemiological characteristics based on the results of nation-wide surveys conducted in 1972 and 1984. Age-adjusted mortality trends based on vital statistics were also examined. The estimated prevalence rate in males increased from 3.0 per 100,000 population in 1972 to 3.8 in 1984 and in females from 3.3 to 5.6, respectively (p less than 0.01), while the estimated incidence rate remained unchanged (1.2 per 100,000 in males and 1.4 in females). The age-adjusted mortality rate showed a gradually decreasing tendency from 0.2 to 0.1 per million. The estimated age-sex specific prevalence and incidence rates showed a pronounced increase in the middle-aged and elderly age groups particularly in females but a marked decrease in those 19 years and under. The increase in prevalence rate may be attributable to the prolonged duration of the disease. Noteworthy changes in the pattern of the disorder included a marked increase in the proportion of patients with eye lesions (males: from 31.3% to 44.4% and females: 41.6% to 58.7%) indicative of poor prognosis and statistically insignificant increase in pulmonary parenchymal lesions (males: from 38.1% to 43.4% and females: from 33.5% to 36.4%), the majority of which showed pulmonary mottling not accompanied with severe fibrosis often seen in Europe and America. The standardized prevalence ratios were observed in hot, warm and cold areas.(ABSTRACT TRUNCATED AT 250 WORDS)