OBJECTIVES: To estimate the maximum potential preventive effect of hip protectors in older persons living in the community or homes for the elderly. DESIGN: Observational cohort study. SETTING: Emergency departments in the Netherlands. PARTICIPANTS: Hip fracture patients aged 70 and older who visited the emergency departments of five hospitals in the Netherlands (n=520). MEASUREMENTS: Using the risk score of the Dutch Guidelines for Osteoporosis, how many patients had a high risk for fractures was retrospectively assessed. In addition, the circumstances of the hip fracture were assessed (n=299). Four factors were specified that might influence the maximum potential preventive effect of hip protectors: (1) hip fracture occurred in persons having a low risk, (2) hip fracture was not the consequence of a fall, (3) hip fracture occurred during circumstances that preclude the use of hip protectors, and (4) hip fracture occurred during the night. RESULTS: When providing hip protectors to women at high risk of fractures, 48.2% of all hip fractures could have been prevented. CONCLUSION: Many hip fractures occur in persons with a low risk for hip fracture or under circumstances that preclude the use of hip protectors. It was estimated that the maximum potential preventive effect of hip protectors is approximately 50% in older women living in the community or homes for the elderly. The actual preventive effect will be lower and depends on the acceptance and effectiveness of hip protectors and adherence to wearing them.