This paper reports a concurrent self-report study of 2,456 office encounters with physicians and/or physician assistants (PAs) in 16 primary care, private practices in Florida. Initial patient assignment to either a physician or PA varies according to demographic and visit-specific characteristics. Patients who are male, younger than 65 years, new patients, seeking help for acute problems, and those who are “walk-in” or “work-in” patients are more likely to be assigned to a PA. Among frequently performed procedures, physicians are more likely to perform the partial histories, partial physicals, and pelvic examinations, as well as counsel patients on diet and psychosocial problems. PAs are more likely to perform the complete physical examinations, record vital signs, conduct diagnostic tests, and perform therapeutic procedures (administer injections, change dressings, etc.). Most tasks performed by PAs receive supervision through chart review raiher than direct oversight. The typical patient visit in a practice employing a PA involves the receipt of services from only one provider. Approximately 50% of patient services are performed by physicians only, while 35% of the services are performed solely by PAs, and 15% are performed by both. Most patients have received care from both the physician and the PA.