Farm machinery is an important contributor to the high rates of occupational injury in agriculture. As part of a population-based case-control study, we studied risk factors for machine-related farm injuries. Case patients were farm residents residing in a geographically defined area of central Wisconsin who experienced a farm injury associated with a tractor, farm implement, or other machine which required medical or chiropractic care from May 1990 through April 1992. Controls were selected from an ad hoc census of farm residents in the same area. Telephone interviews regarding demographic characteristics, safety behaviors, and farming practices were completed for 97.8% of 90 case patients and for 82.8% of 221 control subjects. Personal characteristics significantly associated with an increased risk of machine-related injury included the number of hours worked per week and working primarily as a farmer. Dairy farms, farms with nonresident workers, and large farms were associated with an increased risk of injury while farms with registered cows and farms where cows were fed in the barn even in summer experienced fewer injuries. Based on a logistic regression model, the independent risk factors for machine-related farm injury included hours worked per week (2% increased risk/nonresident workers on farm (odds ratio) (OR) = 2.32; 95% confidence interval (CI): 1.07 to 5.06), cows fed in barn in summer (OR = 0.28; 95% CI: 0.12 to 0.64), and registered cows on farm (OR = 0.36; 95% CI: 0.17 to 0.79). Farm safety practices did not appreciably influence the risk of machine-related farm injury.