OBJECTIVES: This analysis compares the characteristics and processes of technology assessment (TA) in large medical groups and HMOs. METHODS: The survey populations were large medical groups and large HMOs (at financial risk for lives>100,000). Mail and telephone questionnaires were implemented. RESULTS: Survey response rate among medical groups was 54% (39/73). Response rate among HMOs was 43% (41/96). In responding medical groups, TA involves physicians (100%), finance staff (85%), and quality improvement staff (77%). In responding HMOs, medical functions (91%) and pharmacy functions (83%) participate in TA. Medical groups most frequently conduct TA when technology is adopted into clinical practice (88% of respondents) and use TA to help develop guidelines (84%). HMOs conduct TA throughout the product lifecycle and use TA for coverage determinations. Medical groups and HMOs conduct TA on injectable biotechnology products more than any other type of drug. 44% of medical group respondents and 90% of HMO respondents seek outside assistance for TA, with the Agency for Healthcare Research and Quality (AHRQ) as a leading source for medical groups and private TA vendors as leading sources for HMOs. Both medical groups and HMOs consider expert opinion and peer-reviewed journals as the most valuable information sources. CONCLUSIONS: The need to manage legal and financial risk while focusing on clinical practice and patient care drives TA in medical groups. A need to define legally defensible benefits drives TA in HMOs.