Advantages of the use of employer records to assess health and safety impact of shiftwork and accessibility of such records were discussed. The security of hindsight, selection of stable periods, and a well defined historical framework were cited as some of the advantages. Other advantages included easy recognition and recording of significant events, and an established system for monitoring worker health and well being. The following sources of data were described: personnel records, insurance/lost time claims, reported sickness absence, company clinic/dispensary records, and accident reports. The four following areas of concern for data access were considered: the study rationale, the legal ramifications, the mechanics of the study, and the company gain. A number of issues involved in data evaluation were highlighted: disparity between the reported incidence of accidents and illnesses in industry with the actual incidence of events; the policy of companies that allow their employees a given number of excused sick days per year; and the crossover problem in shiftwork. The authors conclude that a record study is free of the more obvious forms of systematic response preconceptions because the subjects of the study are not aware of the eventual hypotheses to be tested.