For the 25 million people in the United States with limited English proficiency, the potential for medical mishaps is multiplied. Too often, however, interpreter services at hospitals and other medical settings are inadequate. According to a study published in March, ad hoc interpreters make nearly twice as many potentially clinically significant interpreting errors as do trained interpreters. The study, published online in the Annals of Emergency Medicine, examined 57 interactions at two large pediatric emergency departments in Massachusetts. Researchers analyzed audiotapes of the visits, looking for five types of errors. They recorded 1,884 errors, of which 18 percent had potential clinical consequences.