Unbiased risk assessment models base health plan payments on enrollee health care needs. We explored the risk structure of employed adult health maintenance organization (HMO) members using the RAND-36 health survey. We used multivariate techniques to estimate risk weights on demographic and health status factors. The dependent variable was annual real total health plan expense for covered services for the year following the survey. Repeated random-split-sample validation techniques minimized outlier influences. Five scales improved prediction over simple demographic factors, but demographic factors still were required to achieve unbiased forecasts. Self-reported health status is a useful and powerful risk measure for adults.