The case history is given of a 6-month-old girl who survived an attack of malignant hyperthermia that occurred during the repair of a cleft lip. We believe that this is the youngest such patient reported to date. The current concepts of the mechanisms of excessive heat production and muscular rigidity are presented. The need for constant awareness, early recognition, and prompt and proper treatment on the part of both the operating surgeon and the anesthesiologist are stressed to avoid a fatal outcome. Unfortunately, as yet there is no conclusive, consistent screening test available to identify those who will experience such an episode. Because a patient has once undergone general anesthesia uneventfully does not mean that malignant hyperthermia will not occur during a subsequent procedure or even during use of some amide local anesthetics.