The purpose of this study was to tabulate the complications encountered in 1650 patients who underwent pediatric transesophageal echocardiography. The occurrence of complications and their type and severity were prospectively recorded. The patients had a mean age of 3.6 years (range 1 day to 21 years) and a mean weight of 17.2 kg (range 1.6 to 118 kg). Of the 1650 cases, 1534 were intraoperative. Most patients studied (97%) had congenital heart disease. Complications occurred in 52 (3.2%) of the 1650 patients. Failure to insert the probe occurred in 13 (0.8%) patients; if those cases are not counted as complications, the incidence of overall complications falls to 2.4%. Airway obstruction occurred in 14 (1%) patients, right mainstem advancement of the endotracheal tube in 3 (0.2%), inadvertent tracheal extubation in 8 (0.5%), vascular compression in 10 (0.6%), and single additional complications in 4 (0.2%). No significant bleeding, arrhythmias, esophageal injuries, or deaths occurred. Failure to insert the probe and airway complications occurred predominantly and significantly in smaller subjects. It is concluded that the incidence of complications during pediatric transesophageal echocardiography is low.