The construction industry is prone to accidents. In Norway there is little research-based knowledge on accident pattern and risk factors. The main objective of the study was to examine whether in-depth studies of accidents in this industry, leading to injuries registered by the health services, could identify preventable risk factors and preventive measures.50 accidents in the construction industry were thoroughly investigated. All had led to serious personal injury. Patients were interviewed after treatment in emergency wards and hospitals in Oslo, and inspections of the accident sites were performed. An interdisciplinary expert group discussed the accidents in order to identify risk factors and suggest preventive measures. The accident reports in the study were compared to reports from the Labour Inspectorate on the same accidents.The investigation identified several risk factors, and a number of detailed preventive measures were proposed. We submitted these proposals to the authorities and organisations involved. Accidents because of time pressure and electricity were two main groups. More than one third of the respondents said that time pressure had contributed to the accident. Accident risk caused by time pressure can be reduced by avoiding piecework contracts, unrealistic time limits, and the use of day penalties for breach of contract. Possible preventive measures for electric injuries imply modification of the reporting system and of the work organisation so that workers can comply with the regulations more easily. The study reports generally contained more information of relevance for prevention than the routine reports from the Labour Inspectorate did. For accidents reported by the Inspectorate to the police, their reports were more informative than the study reports.By the method presented, we obtained detailed information about accidents and preventable risk factors, so that preventive measures could be proposed. The method can also be used for other types of accidents.