In order to study causal factors involved in worker fatalities, the National Institute for Occupational Safety and Health has set up a program to intensively investigate worker fatalities near its Cincinnati, Ohio office. To date, investigations consisting of interviews, reviews of company records, and on-site inspections have been completed for eight fatalities, and certain uniformities have been identified. Although physical hazards were present in each case, apparent deficiencies in management and/or human factors were involved in every fatality. These include inadequate protection against hazards, lack of adequate safety training in recognition and avoidance of safety hazards, inadequate supervision, and lack or violation of safety work rules or procedures. The following three cases exemplify such safety deficiencies. (1) A coal conveyer operator had his arm amputated while greasing the conveyor head (snub) pulley as it was running. Operators had resorted to the unsafe practice of lubricating the pulley while the conveyor was in operation to correct an annoying squeak. Although workers alleged that they had complained to management, the squeak had not been corrected. (2) A truck boom operator was electrocuted when his boom touched a high-voltage power line while unloading bricks at a home construction site. The driver who operated the boom from a metal remote control box, had chosen a poor position from which to drop the load, with poor visibility and too close proximity to the line. Probable causes of the accident were vague work rules, inadequate supervision, driver carelessness, and lack of protective equipment. (3) A drainage foreman was struck by a moving backhoe after he dashed in back of it to check an apparent oil leak. Poor visibility, lack of safe work practices, and lack of backup warning device were the probable causes of this fatality. It is concluded that employer accident reports and statistical surveys offer little insight into accident causation, and that a concentrated in-depth study of selected accidents is more useful.