OBJECTIVE: High exposure to glucocorticoid drugs is associated with an increased risk of osteoporosis and fracture. To define the degree to which individual prescribers needed to adjust their prescribing practices and thus to prevent glucocorticoid-induced osteoporosis among their patients, this research sought to identify both the health plan members who had high exposure to glucocorticoid drugs and the physicians who prescribed these drugs. DESIGN: Patient demographic characteristics, diagnoses, and medications were determined for members of the Kaiser Foundation Health Plan of Northern California who received more than two grams of prednisone (or its equivalent) during any 12-month period from 1998 through 1999. RESULTS: High exposure to glucocorticoid drugs was identified in 22,444 health plan members, accounting for about 1% of adult health plan members. High exposure to glucocorticoid drugs increased sixfold from about 0.5% in members 20-30 years old to about 3% in members 77-79 years old; among these members, 3,788 physicians prescribed the glucocorticoid drugs that led to high exposure. The highest numbers of highly exposed patients were seen among rheumatologists and oncologists. Nephrologists, pulmonologists, and gastroenterologists had an intermediate number of highly exposed patients. Internists had the lowest number of highly exposed patients per physician, yet prescribed glucocorticoid drugs to the largest group (40%) of highly exposed patients in the study. CONCLUSIONS: Using a pharmacy database system developed to identify patients exposed to potentially harmful amounts of glucocorticoid drugs, we identified high glucocorticoid exposure in 1%-3% of health plan members more than 50 years old. In addition, grouping prescribing physicians by medical specialty showed that the need to adjust prescribing practices to prevent glucocorticoid-related complications was unevenly distributed among specialty groups. To improve quality of care for patients in managed care organizations who have high exposure to glucocorticoid drugs, systems for preventive identification and intervention should be developed using pharmacy databases, and should be tailored to physician specialty.