The aim of this study was to assess the effect of nandrolone (Deca-Durabolin, AKZO Nobel, Cambridge, United Kingdom) on mandibular growth in juvenile and adult rats with radiographic cephalometry and immunoradiology. Juvenile (n = 16) and adult (n = 16) inbred female Wistar-Kyoto rats were compared. Each group was divided into 2 subgroups with 8 experimental (E) and 8 control (C) animals in each subgroup. Lateral headfilms taken before and after the 70-day study period were analyzed. Body weight and blood serum IGF-I levels were monitored weekly. The results showed marked mandibular growth changes in both the juvenile and the adult E rats. Body weight increase was larger in the E than in the C animals. The IGF-I blood serum levels were similar in the juvenile E and C rats but higher in the adult E animals than in the adult C animals. It was found that the anabolic steroid (Deca-Durabolin) had a significant effect on mandibular growth in both juvenile and adult rats.