Background: Based upon our clinical observation, many job-related injuries occur as a consequence of workers performing a task or engaging in an activity for which they have not been trained. Methods: A case-crossover study was used to evaluate unusual job tasks, unusual tools and unusual work locations as triggers for occupational injuries. Data on work activities on the day of the injury and 7 days prior to injury were collected via in-person interview. Results: All the 33 subjects enrolled were male, 23 were white and 10 were black, with a mean age of 34.9 years. The most common mechanisms of injury were falls and burns. The most common injuries were fractures and closed head injuries. Unusual job tasks [odds ratio (OR) 27.0, 95% confidence interval (CI) 3.1 - 235.3] and unusual tools (OR 13.3, 95% CI 1.4-125.4) were associated with the injury. Conclusions: Workers should be extra cautious and they should be provided with training for new tasks and new tools. © Society of Occupational Medicine 2005; all rights reserved.