Twelve autistic and schizophrenic children were observed under controlled conditions of high success and high failure on the same task. Two measures of "normal" behavior and three measures of "pathological" behavior were made. "Looking" behavior was not significantly different under the two conditions but tended to be higher during failure. All measures of "pathological" behavior were significantly increased during failure. "Avoidance" behavior showed a significant conditionby-interval interaction with the behavior increasing across time during failure only. A similar trend was found for "self-stimulatory" behavior. Many children dignosed as autistic or schizophrenic may have their level of performance severely limited by brain dysfunction and the "pathological" behaviors considered characteristic of their condition may not be unique to their diagnostic category but may be a function of an unrelieved low success: failure ratio.