Numerous studies suggest that the use of in-person, professionally trained medical interpreters can reduce health care costs associated with diagnosing and treating patients with limited English proficiency. However, few studies have specifically addressed the question of the cost-effectiveness of language services in health care settings. This study used a randomized controlled study design to compare the cost-effectiveness of using professional interpreters with Spanish-speaking patients seen in hospital emergency departments (EDs) versus using the usual language services available to these patients. The main goal of the study was to estimate the effect that professional interpreters have on resource utilization and patient/provider satisfaction in the ED compared to the language services usually offered in these settings. Our hypothesis was that use of trained interpreters would lead to more cost-effective provision of ED services.