BACKGROUND Efforts to address resident errors and to enhance patient safety have included systemic reforms, such as the Accreditation Council for Graduate Medical Education's (ACGME's) mandated duty-hour restrictions, and specialty-specific initiatives such as the neurosurgery Milestone Project. However, there is currently little data describing the basis for these errors or outlining trends in neurosurgical resident error. METHODS An online questionnaire was distributed to program directors of 108 U.S. neurosurgery residency training programs to assess the frequency, most common forms and causes of resident error, the resulting patient outcomes, and the steps taken by residency programs to address these errors. RESULTS Thirty-one (28.7%) responses were received. Procedural/surgical error was the most commonly observed type of error. Transient injury and no injury to the patient were perceived to be the 2 most frequent outcomes. Inexperience or resident mistake despite adequate training were cited as the most common causes of error. Twenty-three (74.2%) respondents stated that a lower post graduate year level correlated with an increased incidence of errors. There was a trend toward an association between an increased number of residents within a program and the number of errors attributable to a lack of supervision (r = 0.36; P = 0.06). Most (93.5%) program directors do not believe that mandated duty-hour restrictions reduce error frequency. CONCLUSIONS Program directors believe that procedural error is the most commonly observed form of error, with post graduate year level believed to be an important predictor of error frequency. The perceived utility of systemic reforms that aim to reduce the incidence of resident error remains unclear.