To assist those responsible for agricultural safety, we: (1) piloted an approach to costing hospitalized farm injuries; and, (2) described ambulance and inpatient costs associated with these injuries in Ontario. Hospital discharge records (hospital separations) for farm machinery injuries in Ontario (n = 1,610) were identified by ICD9-CM E-codes for 1985-1993. Ambulance costs were estimated by the Ontario Ministry of Health. For each case, the hospital costs were calculated by multiplying the case-specific resource intensity weight by the average inpatient cost per weighted case. The costs (1993 Canadian dollars) ranged from $768 to $62,643 and totaled $6.9 million over the study period. Males accounted for 89.8% of the total costs. Tractor injuries accounted for a large proportion of costs (34.3%). The median costs per case varied by type of machinery, ranging from $2,043 for ploughs/disks to $3,366 for augers. Entanglement injuries were responsible for the largest proportion of costs (40.7%), while tractor rollovers accounted for the highest median cost ($3,065). Although these figures represent a fraction of the total costs associated with farm injuries, the results provide one basis from which to justify and target preventive initiatives. This approach to costing may also be widely applicable to other health issues.