Objective: To describe circumstances surrounding injuries involving nail guns among carpenters, calculate injury rates, identify high risk groups and preventive measures. Methods and setting: Active injury surveillance was used to identify causes of injury among a large cohort of union residential and drywall carpenters. Injured carpenters were interviewed by experienced journeymen; enumeration of workers and hourworked were provided by the union. The combined data allowed definition of a cohort of carpenters, their hours worked, detailed information on the circumstances surrounding injuries, and identification of preventive measures from the perspectives of the injured worker and an experienced investigator. Results: Nail guns were involved in 14% of injuries investigated. Ninety percent of these injuries were the result of the carpenter being struck, most commonly by a nail puncturing a hand or fingers. The injury rate among apprentices was 3.7 per 200 000 hours worked (95% confidence interval (CI) 2.7 to 4.9) compared with a rate of 1.2 among journeymen (95% CI 0.80 to 1.7). While not always the sole contributing factor, a sequential trigger would have likely prevented 65% of the injuries from tools with contact trip triggers. Conclusions: Training, engineering, and policy changes in the workplace and manufacturing arena are all appropriate targets for prevention of these injuries. Use of sequential triggers would likely decrease acute injury rates markedly. Over 70% of injuries among residential carpenters were associated with through nailing tasks (such as nailing studs or blocks, trusses or joists) or toe nailing (angled, corner nailing) as opposed to flat nailing used for sheathing activities; this provides some indication that contact trip tools could be used solely for flat nailing.