OBJECTIVE: The objective of this study was to assess the reliability and validity of an objective structured assessment of technical skills (OSATS) for repair of fourth-degree obstetric lacerations on a surgical model. STUDY DESIGN: Three blinded judges reviewed recordings of 20 junior and 20 senior obstetrics-gynecology residents performing simulated perineal repairs using a beef tongue model. Judges completed task-specific OSATS and global rating scales for each repair. Six recordings were rereviewed after 2 weeks. Inter- and intrarater reliability and construct validity were assessed. RESULTS: Interrater reliability was 0.80 for task-specific OSATS and 0.59 for the global rating scale. Intrarater reliability was poor. Construct validity was demonstrated, with senior residents scoring higher than junior residents on task-specific OSATS (13.0 vs 10.5; P = .007) and the global rating scale (24.0 vs 19.3; P = .001). CONCLUSION: We found good interrater reliability and construct validity using a task-specific OSATS for fourth-degree perineal laceration repair. This instrument shows promise as a tool for competency-based evaluations.