Health services research uses increasingly data from health insurance funds. It is well known that the funds differ with regard to sociodemographic characteristics and morbidity. It is uncertain if there are also differences in the prevalence of musculoskeletal disorders. To compare the sociodemographic characteristics in various health insurance funds and the prevalence of joint disorders and chronic back pain. The 30(th) wave (2013) of the German Socioeconomic Panel served as a database. Average age, sex distribution, nationality, education, and employment status were evaluated according to the health insurance funds. The prevalence of joint disorders and chronic back pain were also stratified according to the insurance funds and standardized according to age and sex. A total of 19,146 participants were included. Most participants (4,934) were insured by AOK, followed by BKK (2,632) and BARMER GEK (2,398). There were huge differences among the health insurance funds with regard to the sociodemographic characteristics. For example, the proportion of unemployed insurants was between 33.3 % (IKK) and 50.6 % (AOK). The prevalence of joint disorders standardized according to age and sex (20.7 %; 95 % CI: 20.1-21.3) was between 17.4 % (95 % CI: 15.8-19.0; PKV) and 22.4 % (95 % CI: 21.1-23.6; AOK). The prevalence of chronic back pain (18.0 %; 95 % CI: 17.4-18.5) was between 13.5 % (95 % CI: 12.2-14.9; PKV) and 20.6 % (95 % CI: 19.4-21.8; AOK). There are differences in the prevalence of musculoskeletal disorders among health insurance funds. The extrapolation of analyses of one health insurance fund to the German population is thus limited.