In order to illuminate causes of accidental occupational exposure of the house staff at the Central Hospital of Holstebro (CHH) to the potential hazards of HIV- and HBV-transmission, all cases of reported injuries occurring in 1991-1992 have been analysed. Needleprick lesions were found to account for the great majority of the reported cases (71%). Sixty-six percent of all injuries were self-inflicted during medical procedures, while 34% were caused by another person, either directly (simultaneous contact of two persons with the contaminated sharp object) or indirectly as a result of carelessness or negligence. Seventy-two percent of the analysed exposures could have been avoided if the staff had complied with Universal Precautions recommended since 1988. In order to estimate the amount of unreported cases, all nurses and laboratory technicians currently employed at CHH were asked to complete an anonymous questionnaire reviewing their past (1991-1992) mucocutaneous and percutaneous exposures to blood or body fluids. Only 28% of the injuries recalled by the subjects had been reported. If the risk of occupational transmission of blood-borne diseases is to be minimized, additional effort must be made to clarify the principles of the Universal Precautions policy. It is of great importance that all injuries are reported by way of an easy reporting procedure which is efficient and familiar to the staff at any time.