This study documents the timing of epiphyseal union at the innominate, femur, tibia, and fibula in a sample of modern Portuguese skeletons. The sample was taken from the Lisbon documented skeletal collection and it is comprised of 57 females and 49 males between the ages of 9 and 25. Individuals are mostly representative of the middle-to-low socioeconomic segment of the early 20th century Lisbon population. A total of 18 anatomical locations were examined for epiphyseal union using a three-stage scheme: 1) no union; 2) partial union; and 3) completed union, all traces of fusion having disappeared. Results show that females are ahead of males by 1–2 years and provide similar age ranges for the stages of union than previous studies. Some variations between studies can be explained by methodological differences between dry bone and radiographic observations. However, a review of the literature indicates that socioeconomic status of a given population seems to be of decisive importance to the rate of ossification and most of the differences in skeletal maturation across studies and populations can probably be ascribed to different levels of social and economic development of the societies in which the individuals lived. Although the effects of socioeconomic status in skeletal maturation are greater during childhood than in adolescence, as to make the timing of epiphyseal union a reliable estimate of age at death, they are not negligible and age estimates should take into account the likely socioeconomic status of the individual, whose remains are under examination. Am J Phys Anthropol, 2008. © 2007 Wiley-Liss, Inc.