Background: Many believe that managed care creates pressure on physicians to increase productivity, see more patients, and spend less time with each patient. Methods: We used nationally representative data from the National Ambulatory Medical Care Survey (NAMCS) of the National Center for Health Statistics and the American Medical Association's Socioeconomic Monitoring System (SMS) to examine the length of office visits with physicians from 1989 through 1998. We assessed the trends for visits covered by a managed-care or other prepaid health plan (prepaid visits) and non-prepaid visits for primary and specialty care, for new and established patients, and for common and serious diagnoses. Results: Between 1989 and 1998 the number of visits to physicians' offices increased significantly from 677 million to 797 million, although the rate of visits per 100 population did not change significantly. The average duration of office visits in 1989 was 16.3 minutes according to the NAMCS and 20.4 minutes according to the SMS survey. According to both sets of data, the average duration of visits increased by between one and two minutes between 1989 and 1998. The duration of the visits increased for both prepaid and non-prepaid visits. Non-prepaid visits were consistently longer than prepaid visits, although the gap declined from 1 minute in 1989 to 0.6 minute in 1998. There was an upward trend in the length of visits for both primary and specialty care and for both new and established patients. The average length of visits remained stable or increased for patients with the most common diagnoses and for those with the most serious diagnoses. Conclusions: Contrary to expectations, the growth of managed health care has not been associated with a reduction in the length of office visits. The observed trends cannot be explained by increases in physicians' availability, shifts in the distribution of physicians according to sex, or changes in the complexity of the case mix.