Strokes occurring among persons between 15 and 65 years of age (population 300 000) have been registered since 1970 in Göteborg, Sweden. Control of the validity showed that less than 10% of all cases of stroke were undetected. During the period Nov. 15, 1970-May 14, 1975, 986 stroke events occurred in 941 patients, giving an annual average incidence rate of 73 (89 for men and 58 for women) per 100 000 individuals 15-65 years of age. The incidence for all ages was estimated to be about 200/100 000. The rates were higher for men than for women in all age groups. There was a female preponderance for subarachnoid haemorrhage but a male preponderance for other types of stroke. Incidence rates increased with age, most rapidly for brain infarcts and unspecified stroke. Fatality rates levelled out 3 weeks after onset of stroke; they were high for subarachnoid and intracerebral haemorrhage and low for cerebral infarction and unspecified stroke. Incidence rates were lower than those found in two similar studies from Denmark and Finland, and even greater variations were found with respect to types of stroke. Fatality rates were similar to those reported by other authors.