AbstractObjective To examine differences in the characteristics of adverse events between English speaking patients and patients with limited English proficiency in US hospitals. Setting Six Joint Commission accredited hospitals in the USA. Method Adverse event data on English speaking patients and patients with limited English proficiency were collected from six hospitals over 7 months in 2005 and classified using the National Quality Forum endorsed Patient Safety Event Taxonomy. Results About 49.1% of limited English proficient patient adverse events involved some physical harm whereas only 29.5% of adverse events for patients who speak English resulted in physical harm. Of those adverse events resulting in physical harm, 46.8% of the limited English proficient patient adverse events had a level of harm ranging from moderate temporary harm to death, compared with 24.4% of English speaking patient adverse events. The adverse events that occurred to limited English proficient patients were also more likely to be the result of communication errors (52.4%) than adverse events for English speaking patients (35.9%). Conclusions Language barriers appear to increase the risks to patient safety. It is important for patients with language barriers to have ready access to competent language services. Providers need to collect reliable language data at the patient point of entry and document the language services provided during the patient–provider encounter.