The injury severity score (ISS) has been most widely accepted as a practicable method of classifying traumatised patients (ie., patients with accident injuries) according to the severity of their injuries, and has become more popular than all other comparable classification systems. By allocating the patients to different severity groups, it facilitates their classification in respect of prognosis. Over and above this, it enables comparison of patient groups of different hospitals. The authors investigated the validity of ISS classification by studying the case records of 432 patients in a traumatological intensive-care ward. They found good correlation between ISS score on the one hand, and lethality, requirements of banked blood during first-aid care and duration of treatment and artificial respiration of survivors on the other. However, the mean survival time of those patients who had died, did not reveal any connection with the severity of the injury. It is definitely impossible to arrive at any prognosis for an individual patient on the basis of his ISS classification. With increasing age, lethality after an accident increases even if the injury is less severe. The validity of ISS could be increased further if the age of the patients could be taken into account as well.