In this study, the accuracy of regression equations of developing permanent tooth length for age estimation (Liversidge and Molleson. J Forensic Sci. 1999;44:917) is tested on a sample of 88 Portuguese juvenile skeletons of known age at death. Results reveal an overall high accuracy for the method, showing an average difference between estimated and chronological age between 0.56 and 0.05 years, when using single teeth and 0.16 years, when using all available teeth. Accuracy tests indicate that age estimates can be obtained within ±0.17 years with a 95% confidence interval when several teeth are used. Overall between-tooth agreement in age estimates decreases with increasing age but there is less variability of estimates with more teeth contributing to overall mean age. However, there is a tendency for overestimation of age of younger individuals (<6 years) and of age obtained from half of the dentition. Although the advantages of this technique probably make it the preferred method of age estimation of human immature skeletal remains, when microstructural methods are not an option, a possible positive secular trend effect and differences in socioeconomic conditions detected between populations may warrant caution in its applicability to modern forensic cases.