Background Large numbers of claim files present a potentially valuable source of information to get insight on possibilities for prevention of claims. Therefore, the feasibility of root cause analyses on incidents leading to liability claims at The Netherlands' largest medical liability insurer was assessed. Methods Feasibility was defined by validity, reliability and applicability. Claim files from diagnostic errors in emergency departments of Dutch hospitals were selected. All closed and settled claim files from the year 2001 and 2002 were used. Results Fifty incidents occurring at 31 emergency departments were found in 47 files. 114 root causes were found, on average 2.3 per incident. 78% of the incidents were related to missed fractures, luxations or tendon lesions. Zero technical, 29% organisational, 66.7% human-related and 4.4% patient-related factor errors were found. Inter-rater agreement for classification of root causes was good (k¼0.78). Preventive measures following from Prevention and Recovery Information System for Monitoring and Analysis (PRISMA) classificationeaction matrix were improving completion of available sources of information, improving structures of communication and training staff to prevent failures due to the wrong implementation of tasks or due to errors in reasoning. Discussion Validity of the root cause profile of diagnostic claims is considered moderate because of a lack of information about technical and organisational causes of errors. Therefore, the root cause profile was incomplete for organisational factors in comparison with other studies. However, with regard to the diagnostic reasoning process, the profile was stable. The feasibility of PRISMA for retrospective analyses of closed claims may be improved if system-based reasoning by the liability insurer and hospital staff is enhanced.Learning from incidents by means of root cause analysis is one of the key elements of programmes or institutions aiming to improve patient safety.