Background and objectives. The number of US residents with limited English proficiency (LEP) is 14 million and rising. The goal of this study was to estimate the effects of LEP on physician time and resource use. Design. This was a prospective, observational study. Setting and Subjects. The study included 285 Medicaid patients speaking English (n = 112), Spanish (n = 62), or Russian (n = 111) visiting the General Medicine and Family Practice Clinics at the UC Davis Medical Center in 1996-1997 (participation rate, 85%). Bilingual research assistants administered patient questionnaires, abstracted the medical record, and conducted detailed time and motion studies. Main outcome measures. We used seemingly unrelated regression models to evaluate the effect of language on visit time, controlling for patient demographics and health status, physician specialty, visit type, and resident involvement in care. We also estimated the effect of LEP on cross-sectional utilization of health care resources and adherence to follow-up with referral and testing appointments. Results. The 3 language groups differed significantly by age, education, and reason for visit but not gender, number of active medical conditions, physical functioning, or mental health. Physician visit time averaged 38+/-20 minutes (mean+/-SD). Compared with English-speaking patients and after multivariate adjustment, Spanish and Russian speakers averaged 9.1 and 5.6 additional minutes of physician time, respectively (P P = 0.003) and Spanish speakers were less likely to follow-up with recommended laboratory studies (P = 0.031). Conclusions. In these academic primary care clinics, some groups of patients using interpreters required more physician time than those proficient in English. Additional reimbursement may be needed to ensure continued access and high-quality care for this special population.