Using data obtained from a statutory health insurance (AOK) in the federal state of Lower Saxony, this study examined whether there were differences between the insured population compared with that of Lower Saxony (Niedersachsen) and of Germany with respect to social structural characteristics. Data for the comparisons were provided by the statistical office of Germany, and all datasets were coded according to the same criteria. The differences in gender distribution and age distribution between the AOK, Lower Saxony, and Germany were small. The share of employed individuals among the insured compared with those of Lower Saxony and Germany did not differ for males, but it was lower in women. In the insured population a higher proportion of individuals had lower qualification levels than in Lower Saxony or in Germany; the number of individuals with higher qualifications was, however, sufficient to permit statistical analyses. There were differences in the distributions of social structural characteristics between the health insurance population on the one hand and the populations of Lower Saxony and of Germany on the other. Due to the high number of cases, it is nevertheless possible to analyze associations between social structural variables, health impairments, and patterns of health care utilization.