This article describes travel patterns for ambulatory care based on the 1978 National Health Interview Survey. The county where a physician visit occurs has been compared with the county of patient's residence. Nearly 20 per cent of physician visits occur outside the county of residence, with substantial variation according to metropolitan status and proximity to an SMSA. Visits by nonmetropolitan residents are twice as likely to occur in another county as visits by metropolitan residents. The proportion of visits that occur outside the county of residence increases with decreasing population density, both among metropolitan and nonmetropolitan areas. Travel patterns for the usual source of care are similar to those for primary care physician visits. The results are used to estimate adjusted physician-population ratios by allocating physicians to each county type in proportion to their use by residents. These adjusted ratios exhibit substantially less variation than the unadjusted ratios.