BACKGROUND AND OBJECTIVE There is a strong relationship between neuromuscular activity and facial skeletal morphogenesis. The systemic use of anabolic steroid accelerates craniofacial growth and induces high functional activity of rats' masticatory muscles. The present study examines the effect of an anabolic steroid locally applied in the masseter muscle of growing rats with the purpose of verifying possible craniofacial changes with minimum drug side effects, using cephalometric analysis. MATERIALS AND METHODS Forty-three 3-week-old Wistar rats were evaluated and divided into two groups: (1) NAN group (local bilateral masseter injection of nandrolone decanoate - 0.05 microg/3 microl/bi-weekly) and (2) CON group (local bilateral masseter injection of sterile oil - 3 microl). Tukey and Wilcoxon tests were used. RESULTS In NAN group the cephalometric measures showed horizontalized facial growth (reduce of FMA angle -p<0.01), increase of posterior facial height, decrease of anterior facial height, reduction of gonial angle (p<0.05), increase of mandibular height (p<0.01). There was no variation in the length of the mandible, in the skull and animals' weight gain, thus demonstrating that no important systemic effect occurred. CONCLUSION The local injection of nandrolone in the masseter muscle of rats was capable to alter the growth direction and the morphology of the craniofacial complex in Wistar rats.