Farm machinery is a major cause of injury morbidity and mortality among farmers. This case-control study assessed risk factors for machinery-related injuries among Iowa farmers. A screener questionnaire sent to 6,999 farmers in 1998 identified 205 farmers who had machinery-related injuries requiring medical advice/treatment in the previous year. Possible risk factors for injury were assessed among these farmers compared with 473 farmers with no injury in the previous year. A multiple logistic regression analysis showed significant associations between machinery-related injury and hours per week spent on farmwork (OR = 2.02; 95% CI 1.38-2.94), fewer years of farming experience (OR = 1.79; 95% CI 1.14-2.79), wearing a hearing aid (OR = 4.37; 95% CI 1.55-12.25), and a high CAGE score suggesting problem drinking (OR = 2.49; 95% CI 1.00-6.19). This is the first study to show associations between machinery-related injury and hearing impairment, problem drinking, and fewer years of farming experience. These findings may be useful for future interventions to decrease injuries related to farm machinery.