The prevalence and incidence of diabetes mellitus were studied from 1972 to 1987 in Laxå, a rural community with 8500 inhabitants located in mid-Sweden. Data were collected from clinical records at the primary health care centre in Laxå, from departments of internal medicine and paediatrics and from a general practitioner's office in the area. In addition, a case finding procedure involving 85% of the residents aged 35-79 years was performed in 1983-1987. The age-standardized prevalence of diabetes rose significantly (p less than 0.001) from 26 per 1000 in 1972 to 43 per 1000 in 1987. The largest rise in prevalence for males occurred in the age group 45-54 years and for females in the age group 65-74 years. The age-standardized mean annual incidence of diabetes was 3.46 per 1000 population. A small (non-significant) increase in incidence of Type 2 diabetes over time was seen in men which may in part be an effect of the case finding strategy. The overall incidence rates thus appeared to be rather stable while the prevalences tended to increase, probably mainly due to earlier detection of diabetic individuals in recent years, leaving a larger number of patients with a longer duration of diabetes to be cared for in the future.