OBJECTIVE: To describe the proportion of frequent attenders among primary health care patients and their sociodemographic characteristics, morbidity and reasons for encounter. DESIGN: A cross-sectional case-control study. SETTING: A municipal health centre in Oulainen, a small rural town in northern Finland. PARTICIPANTS: Three hundred and four frequent attenders (eight or more visits to health centre physicians (GPs) during the year 1994) and 304 age- and sex-matched controls. MAIN OUTCOME MEASURES: Sociodemographic characteristics, numbers of encounters, chronic diseases classified by ICD-9 and reasons for encounter coded by the International Classification of Primary Care chapter codes (ICPC). RESULTS: 4.7% of the population aged 15 years or older and 6.8% of the annual patients were frequent attenders and they made 23.5% of all encounters with GPs. The frequent attenders had lower basic education and there were more people on disability pension among them. They had significantly more mental disorders and diseases of the musculoskeletal and digestive systems than the controls. The frequent attenders' most common reasons for encounter were musculoskeletal problems, and they had significantly more musculoskeletal, digestive system and psychiatric reasons for encounters than the controls. CONCLUSIONS: Frequent attenders express more somatic and less psychiatric reasons for encounter than can be assumed according to their morbidity. The role of somatization is discussed.