To examine selection bias in terms of demographics, self-reported health practices, professionally evaluated health status, and prior health care utilization by employees and dependents, we examined health insurance choice between traditional insurance and a health maintenance organization (HMO) by central office employees of a large southwestern utility company. The HMO attracted a relatively younger and female population compared with the traditional plan. We found no difference in health practices and health status measures between the two groups. Consistent with recent studies, the HMO group experienced lower health claims cost the year prior to enrollment compared with persons who remained in the traditional plan. This difference was largely due to dependents' utilization-a factor that should be examined in future studies and considered by those structuring insurance premiums for HMOs and traditional plans.