Aim: To explore the effects of mandibular protrusive appliance therapy on condylar position within the fossa. This clarification is needed, because it has been repeatedly reported in the literature that mandibular protrusive appliances cause a forward and downward condylar movement, as a treatment effect, within the fossa. Methods: Pretreatment and posttreatment lateral corrected tomograms of 35 children were used for this study. The children were diagnosed suitable for treatment with a mandibular protrusive appliance (activator). Of the 35 children, 18 were boys and 17 were girls. The mean age at the beginning was 11.56 (± 1.85) years. The tomograms were digitized on the screen by using a commercial software program, and certain linear and angular measurements were made. Furthermore, the orientation of the Frankfort horizontal plane was transferred to each tomogram from the corresponding cephalograms. Paired t tests were applied between initial and final values, separately for left and right sides. Paired t tests were also done between left and right sides to test any left and right asymmetry. Results: The results showed that there was no statistically significant difference for all comparisons employed. However, there was a clear tendency toward inferior and less anterior than initial condylar positioning, although this was not statistically significant. Conclusion: It is concluded that mandibular protrusive appliances do not change, at least to a statistically significant level, the condylar position within the fossa.World J Orthod 2003;4:243–249.