The objective of this study is to compare the likelihood of hospitalization for conditions that are related to the adequacy and use of ambulatory health care services for Medicare beneficiaries residing in rural and urban regions in Utah. The Health Care Financing Administration's (HCFA) hospital discharge database (Utah hospitals: 1990 to 1994) was used to estimate hospitalization rates (with adjustment for out-of-state admissions) for ambulatory care sensitive conditions. Population estimates were obtained from HCFA beneficiary files. Regional hospitalization rates were obtained through ZIP code matching of the hospital discharge and beneficiary files. Medicare beneficiaries aged 65 and older residing in Utah during 1990 to 1994 are the subjects for the study. The main outcome measures include age and sex-adjusted hospitalization rates by region for the entire state and rate ratio estimates for nonurban regions. The results of the study show that Medicare beneficiaries residing in two rural-frontier regions were more likely than urban beneficiaries to be hospitalized for ambulatory care sensitive conditions. Rate ratio estimates were greater than 1.4 for both regions during the study period. These findings suggest a pattern of an increased burden of avoidable secondary complications and disease progression among Utah Medicare beneficiaries residing in some rural regions. This increased burden may be the result of limitations in the ambulatory care system, medical care provider supply, and/or beneficiary propensity to seek care. Variation in disease prevalence or hospital use patterns for these conditions also may be responsible for all or part of the observed variation in ambulatory care sensitive admission rates.