To develop a valid and reliable tool to objectively measure surgical skill necessary for repair of fourth-degree perineal lacerations and then to use this tool to measure improvement after a workshop. We measured baseline surgical ability and clinical knowledge of 26 residents (postgraduate year [PGY]-1 to PGY-4) using the Objective Structured Assessment of Technical Skills (OSATS) and a written examination. The OSATS consists of a global surgical skills assessment (OSATS-G), a procedure checklist (OSAT-C), and pass/fail grade. Five weeks after our baseline evaluation, a 1.5-hour workshop was administered to approximately half of the 26 residents (n=14). One week after this intervention, the residents were re-examined using the same assessment tools. The OSATS demonstrated construct validity as scores on the examination increased on both the OSATS-G and the OSATS-C from PGY-1 through PGY-4 (P=.001 and P=.041, respectively). Reliability indices for the OSATS were high. Eighty-one percent of the residents failed the OSATS before intervention because of failure to identify and repair the internal anal sphincter. After educational intervention, senior residents improved on all assessments (OSATS-G, P=.041; OSATS-C, P=.004; written examination, P=.008), and all residents passed the OSATS. A valid and reliable OSATS and written examination were developed to assess surgical skills, knowledge, and judgment necessary to properly manage fourth-degree perineal lacerations. Residents improved on the OSATS and the written examination after undergoing a structured educational workshop. II.