PURPOSE To determine whether measurements obtained by partial coherence interferometry (PCI) correlate well with measurements obtained using immersion ultrasound (US) in children. SETTING Department of Ophthalmology, Emory University School of Medicine, Atlanta, Georgia, USA. DESIGN Evaluation of a diagnostic test or technology. METHODS The charts of pediatric patients who had cataract surgery from August 2008 to September 2009 were reviewed. Axial length (AL) measurements in the operative eye were obtained using PCI at the preoperative clinic visit and then using immersion US in the operating room before surgery. The data were compared to determine the degree of agreement. RESULTS The charts of 18 patients (27 eyes) were reviewed. Preoperative AL measurements by PCI were obtained in 21 eyes (78%). On average, the PCI-measured ALs were 0.1 mm less than the immersion US values (95% confidence interval, −0.2 to −0.1; P = .002). All eyes with an AL of 23.5 mm or less had lower PCI values than immersion US values. There was no systematic pattern of 1 measurement being greater or less than the other in eyes with an AL longer than 23.5 mm. CONCLUSIONS There is a systematic difference in AL measurement between PCI and immersion US, with PCI tending to give lower values, particularly in eyes with an AL longer than 23.5 mm. Depending on the length of the eye, a 0.1 mm error in AL measurement could result in a 0.25 to 0.75 diopter difference in intraocular lens calculation that could be clinically significant in some patients.