No data exists for the optimal head position during transesophageal echocardiography (TEE) probe insertion in children. Turning the head to the side closes the ipsilateral pyriform sinus and dilates the contralateral pyriform sinus, theoretically making probe insertion safer and easier. In this study, 94 children (weight, <or=10 kg) undergoing TEE during heart surgery between March 2000 and August 2001 were studied. The head position was either midline or left. A scale was devised to grade the resistance during probe insertion: grade 1 (none), grade 2 (mild), grade 3 (moderate), grade 4 (severe), and grade 5 (inability to insert probe). Probe insertion was midline in 38 and left in 56 of the children. Mild or no resistance was encountered in 86% of the head left versus 63% of the head midline children (p = 0.002). Probe insertion was easier with the head left in three subgroups: I (weight, >5 kg), II (weight, 4-5 kg), and III (weight, <4 kg). The difference was statistically significant only for subgroup III (p = 0.0001). Insertion failed in four children with the head in the midline position but was successful when the head was turned leftward. Children undergoing TEE who weigh less than 10 kg should have the head positioned to the side rather than in the midline position during probe insertion. If insertion is unsuccessful or difficult with the head in the midline position, the authors recommend turning the head to the side and reattempting probe insertion.