The purpose of this study was to describe clinical encounters in primary care research networks and compare them with those of the National Ambulatory Medical Care Survey (NAMCS).Twenty US primary care research networks collected data on clinicians and patient encounters using the Primary Care Network Survey (PRINS) Clinician Interview (PRINS-1) and Patient Record (PRINS-2), which were newly developed based on NAMCS tools. Clinicians completed a PRINS-1 about themselves and a PRINS-2 for each of 30 patient visits. Data included patient characteristics; reason for the visit, diagnoses, and services ordered or performed. We compared PRINS data with data obtained from primary care physicians during 5 cycles of NAMCS (1997-2001). Data were weighted; PRINS reflects participating networks and NAMCS provides national estimates.By discipline, 89% of PRINS clinicians were physicians, 4% were physicians in residency training, 5% were advanced practice nurses/nurse-practitioners, and 2% were physician's assistants. The majority (53%) specialized in pediatrics (34% specialized in family medicine, 9% in internal medicine, and 4% in other specialties). All NAMCS clinicians were physicians, with 20% specializing in pediatrics. When NAMCS and PRINS visits were compared, larger proportions of PRINS visits involved preventive care and were made by children, members of minority racial groups, and individuals who did not have private health insurance. A diagnostic or other assessment service was performed for 99% of PRINS visits and 76% of NAMCS visits (95% confidence interval, 74.9%-78.0%). A preventive or counseling/education service was provided at 64% of PRINS visits and 37% of NAMCS visits (95% confidence interval, 35.1%-38.0%).PRINS presents a view of diverse primary care visits and differs from NAMCS in its methods and findings. Further examinations of PRINS data are needed to assess their usefulness for describing encounters that occur in primary care research networks.