Quantitative assessment of patient data is a pertinent part of controlled clinical studies. When several centers are involved, the degree of agreement between different observers becomes important. Therefore, in addition to developing a multicenter study on acute ischemic stroke, we have estimated the interobserver agreement expressed in terms of kappa statistics. Twelve patients suffering from neurologic deficits due to acute ischemic stroke were examined by four investigators, and the results were assessed using the Mathew scale. Considerable interobserver variability was found. Agreement on items based on subjective information from the patient was low, and it is also possible that this information changes with time. It is advised that in the development of assessment scales, items with low interobserver agreement should be avoided.