Skeletal maturation is divisible to three main components; the time of appearance of an ossification center, its change in morphology and time of fusion to a primary ossification center. With regard to the knee, the intermediate period between appearance and fusion of the ossification centers extends over a period of greater than 10 years. This study aims to investigate radiographically the age at which morphological changes of the epiphyses at the knee occur in a modern Irish population. Radiographs of 221 subjects (137 males; 84 females) aged 9–19 years were examined. Seven nonmetric indicators of maturity were assessed using criteria modified from the Roche, Wainer, and Thissen method and Pyle and Hoerr's atlas of the knee. Reference charts are presented which display the timeline for each of the grades of development of the seven indicators. Mean age was found to increase significantly with successive grades of development of each of the seven indicators. A significant difference was noted between males and females at the same grade of development for six of the seven indicators. The narrowest age range reported for a single grade of development was 2.2 years for Grade 2 of development of the tibial tuberosity for males. The information on changing morphology of the epiphyses at the knee in the present study may provide an adjunct to methods used for evaluation of skeletal maturity before surgery for orthopedic disorders or to evaluate skeletal age in clinical scenarios where either delayed or precocious skeletal maturation is suspected. Clin. Anat. 26:755–767, 2013. © 2012 Wiley Periodicals, Inc.