QUESTIONS UNDER STUDY The aim of the study was to analyse the effects of supplementary health insurance on the incidence of hospitalisations for musculoskeletal conditions in Switzerland. METHODS Cross sectional and small area analyses of surgical interventions for major musculoskeletal disorders in Switzerland were conducted. The regional distributions of populations with basic and basic plus supplementary insurance were estimated using census data for the period of 2002-2005. Effects of insurance class on the incidence of orthopaedic interventions were calculated with logistic regression using the complete discharge dataset of hospitalisations for orthopaedic conditions performed in the years 2002 to 2005. RESULTS The data show significant differences in the age- and gender-adjusted incidence of surgery between populations with compulsory basic health insurance and those with basic plus supplementary cover. CONCLUSIONS The study provides evidence that health insurance status accounts for variation in surgery for musculoskeletal problems in Switzerland. There are indications that supplementary health insurance - as a proxy for higher socioeconomic status - is related to lower need for surgery. There are signs that resources for spinal surgery and arthroscopy are diverted to the private sector at the expense of social health insurance. The results are only partially consistent with the hypothesis that volume of services increases with comprehensiveness of coverage.