Expert opinions have an important place for expert testimony in medical disputes. The report should contain a summary about facts and causality between the damage and the medical treatment in question as well as describe the current medical standard. The fulfillment of scientific criteria was investigated in 179 anesthesiological expert opinions from 150 arbitration cases. Anesthesiological expert reports (2005-2007) of the Arbitration Board of the North German Medical Associations were analyzed in terms of structure, general form of assessment and scientific substantiation of statements. Patient damage was confirmed in 76%, treatment failure in 29% and negligent malpractice in 17% of the reports. In 78% of the reports the facts were presented correctly and in 64% the question was answered whether the incident would have occurred even during adequate and professional action. Conclusive statements about the causality between the damage and the medical treatment in question were available only in 60% of the reports. The study findings suggest that anesthesia expert reports present a high incidence of non-scientific claims. The development of guidelines for expert witnesses by the medical societies is urgently recommended.