The purpose of this article is to examine the level of sexual dimorphism exhibited in the foramen magnum and occipital condyles of juveniles, and to test the utility of this sexual dimorphism for estimating sex. Using five basicranial measurements taken from 36 juveniles of known sex and age from the Lisbon documented collection (Portugal), we evaluated sexual dimorphism in the juvenile cranial base. Our application of a method previously applied solely to adults indicated that the basicranium is sexually dimorphic in juveniles, with larger foramen magnum and occipital condyle dimensions observed in males. Significant univariate differences between males and females were found for length and breadth of the foramen magnum, and breadth of the left occipital condyle. Using these measurements, multivariate discriminant analysis indicated that sex was correctly assigned 75.8% of time. Obtained accuracy, however, was lower than reported by previous studies of adult samples. We suggest that this discrepancy is a result of population variability rather than age. Am J Phys Anthropol 2010. © 2009 Wiley-Liss, Inc.