Gradually there are increasing tendencies toward Cesarean sections, either intentionally or inevitably. Since two lives are simultaneously in one case, we must make all efforts to administer anesthesia even more cautiously for Cesarean section patients than for other cases. Occasionally, grave problems occur during induction of anesthesia, especially in general anesthesia. Among them, one of the most serious accidents is aspiration of the stomach contents into the lungs by vomiting or regurgitation. This may induce severe complications, such as chemical pneumonitis due to aspiration of liquid acid contents and/or death due to asphyxia of solid materials. Already several decades ago Mendelson and other authorities described a lung syndrome which was associated with aspiration of vomitus in various degrees of acidity. In an emergency Cesarean section, the authors experienced a case of Mendelson's syndrome which was produced by aspiration of liquid acid stomach contents because of an intubation mistake. Immediately after the operation. the patient began to complain of severe respiratory discomfort and a febrile state which continued for several days post-operatively. However, because of intensive nursing care with oxygenation, intermittent positive pressure breathing, large doses of steroids and antibiotics, the patients condition was restored from the acute febrile stage to the pre-operative level. Within five days the chest X-ray films were normal and on the seventh day the patient and her baby were discharged in good condition. We would like to conclude that many different kinds of drugs and/or methods of anesthesia are not alone sufficient in managing dangerous situations, such as energency Cesarean section but intensive pre-operative care and highly proficient techniques are essential as a prophylactic method in undesirable complications.