BACKGROUND: The purpose of this study was to investigate the usefulness of ultrasonography (US) for confirmation of endotracheal tube (ETT) placement during resuscitation in extremely low birthweight (ELBW) infants. METHODS: We conducted a retrospective review of the medical records of ELBW infants in whom ETT position was verified using US between June 2016 and September 2017. We investigated the backgrounds of the patients and US investigators, and the time required for the detection of exhaled carbon dioxide using the colorimetric method and US. RESULTS: Eleven ELBW infants were evaluated using US by four neonatologists. The median duration required to determine the ETT position by the colorimetric method and US were 11 s and 3 s, respectively. In six ELBW infants, we were able to verify the ETT position more rapidly using US than using the colorimetric method, and were able to perform prompt resuscitation. Unnecessary reintubations were avoided in three ELBW infants. CONCLUSION: Ultrasonography allowed the swift confirmation of the tracheal intubations. The colorimetric method yielded false negative results; in such cases, unnecessary reintubation could have been avoided if US was used. We assessed the mechanism of false negative results and performed appropriate resuscitation.