The atlantodental interval (ADI) is assessed after trauma to the head and neck region to determine whether the transverse ligament of the atlas is intact. Atlantodental interval measurement from conventional screen-film radiographs is characterized by the need for magnification correction and by low reliability. Assessment of normal ADI values using digital radiography with computer-assisted measurement has not been reported. We compared with published values the digital radiographic measurements of ADI in children, examined the reliability of measurements, and examined the interaction between age, sex and ADI. Computer-assisted digital measurements of ADI in 101 children, aged 1 to 12 years, were obtained from lateral supine head-neutral radiographs. We found intraobserver reliability of 0.72 and 0.85, interobserver reliability of 0.50, a maximum ADI value of 3.5 mm, no effect of sex and age, and weak evidence for an interaction between sex and age. Computer-assisted digital ADI measurement provides higher intraobserver reliability than what has previously been reported, and interobserver reliability and a maximum ADI value similar to that found in the literature.