Aims: Prevalence and risk factors of osteoarthritis in the carpometacarpal joint of the thumb have been amply explored in previous studies. However, no study has focused on CMC OA as a predictor of disability and mortality. We investigated CMC OA for its associations with risk factors, disability and with life expectancy in a extensive health survey. Methods: In 1978–80, a representative population sample of 8,000 Finns aged 30 or over were invited to participate in a comprehensive health examination; 90% complied. Hand radiographs were taken from 3,595 subjects and the clinical status was completed for 3,434 subjects. By the end of 1994, 897 subjects with hand radiographs had died. Results: The age adjusted prevalence rate of CMC OA of Kellgren’s grade 2 to 4 was 7% for men and 15% for women. Adjusted for alleged risk determinants, body mass index was directly proportional to the prevalence of CMC OA in both sexes, OR =1.29 (95% confidence interval 1.15–1.43) per each increase of 5 kg/m2 in body mass index. Smoking seemed to carry a protection against CMC OA in men but not in women. No significant association was found between history of workload and CMC OA. Restricted mobility, tenderness and swelling were frequently found in the presence of radiological CMC OA, but no significant increase occurred in the prevalence of disability. In men CMC OA of Kellgren’s grade 3 to 4 significantly predicted total mortality (adjusted relative risk 1.32, 95% confidence interval 1.03–1.69). Conclusion: In line with previous studies, body mass index strongly determines the prevalence of CMC OA. CMC OA is highly prevalent, but its impact on disability in the general population is scanty.