OBJECTIVE: To establish basic epidemiological data on chronic pain (duration > 3 months) in a defined population. Relationships between age, gender, and social class were tested. DESIGN: A survey of pain symptoms, including location, intensity, duration, and functional capacity, was conducted by means of a mail questionnaire. SETTING: General populations in two Swedish primary health care districts. Medical care was provided in a state health system. SUBJECTS: A random sample (from the population register) of 15% of the population aged 25-74 (n = 1,806). The response rate was 90%. OUTCOME MEASURES: Descriptive epidemiologic data in relation to objectives of the study. RESULTS: Without sex differences, 55% (95% confidence interval, 53-58%) of the population had perceived persistent pain for 3 months and 49% for 6 months. Among individuals with chronic pain, 90% localized their pain to the musculoskeletal system to a variable extent. Women experienced more multiple localizations of pain and had pain in the neck, shoulder, arm, and thigh to a greater extent than men. Prevalence of pain increased by age up to 50-59 years for both genders and then slowly decreased. The neck-shoulder area was the most common site of pain (30.2%), followed by the lower back (23.2%). Even in the youngest age groups more than one of four reported chronic pain. Blue-collar workers and employers (including farmers) reported chronic pain to a greater extent than other groups. In 13% of the population, manifest pain problems were associated with reduced functional capacity. CONCLUSION: Chronic pain symptoms are common but unevenly distributed in a general population. The results may influence planning and consultation in primary health care as well as warranting selective prevention activities.