To measure the differences in direct health care costs and resource utilization among female enrollees in a health maintenance organization who were aged 45 through 65 years and had either osteoporosis or an osteoporosis-related fracture. One year of medical and pharmacy claims (October 1, 1998, to September 30, 1999) from a mixed-model health plan located in the Midwest were evaluated. Diagnoses were determined from medical claims with ICD-9 codes specific to either osteoporosis or osteoporosis-related fracture. Aggregate costs specific to osteoporosis were compared to all costs incurred by the members regardless of the disease states. We identified 600 women who had consumed a total of $4.6 million in health care resources and $411,684 in direct costs specifically related to osteoporosis. The highest total average disease-specific costs were found for women with a fracture ($939 per patient per year [PPPY]) compared to those with osteoporosis only ($645 PPPY). Outpatient costs accounted for the highest percentage of mean total annual costs of care, representing up to 38% of the total health care resources consumed. Average medical costs for women with a fracture were highest for the 60 to 64 years age category, the oldest age category in the study population ($17,403 PPPY, P=.0379). Estrogen was the most utilized drug for treatment of osteoporosis, accounting for 41% of the total osteoporosis-specific prescription utilization. The costs of care for members with osteoporosis-related fractures were, on average, higher than for women with osteoporosis only. The component costs included outpatient services, inpatient services, and prescription costs. Women not receiving drug therapy for management of osteoporosis incurred slightly higher total health care costs than women who did not receive drug therapy for osteoporosis.