The Organ Injury Scaling (O.I.S.) Committee of the American Association for the Surgery of Trauma (A.A.S.T.) was appointed by President Trunkey at the 1987 Annual Meeting. The principal charge was to devise injury severity scores for individual organs to facilitate clinical research. The resultant classification scheme is fundamentally an anatomic description, scaled from 1 to 5, representing the least to the most severe injury. A number of similar scales have been developed in the past, but none has been uniformly adopted. In fact, this concept was introduced at the A.A.S.T. in 1979 as the Abdominal Trauma Index (A.T.I.) and has proved useful in several areas of clinical research. The enclosed O.I.S.'s for spleen, liver, and kidney represent an amalgamation of previous scales applied for these organs, and a consensus of the O.I.S. Committee as well as the A.A.S.T. Board of Managers. The O.I.S. differs from the Abbreviated Injury Score (A.I.S.), which is also based on an anatomic scale but designed to reflect the impact of a specific organ injury on ultimate patient outcome. The individual A.I.S.'s are, of course, the basic elements used to calculate the Injury Severity Score (I.S.S.) as well as T.R.I.S.S. methodology. To ensure that the O.I.S. interdiffuses with the A.I.S. and I.C.D.-9 codes, these are listed alongside the respective O.I.S. Both the currently used A.I.S. 85 and proposed A.I.S. 90 are provided because of the obligatory transition period. Indeed, A.I.S. 90 contains the identical descriptive text as the current O.I.S.'s. The Abdominal Trauma Index and other similar indices using organ injury scoring can be easily modified by replacing older scores with the O.I.S.'s.(ABSTRACT TRUNCATED AT 250 WORDS)