Stuttering is a multi-factorial speech disorder characterized by various dysfluencies in the beginning and/or smooth flow of speech. Its incidence is about 1% in the general population, with 80% of stuttering cases seen in children aged three to eight years. The etiology of developmental stuttering has not been precisely explained. Several researchers report that neurological factors, especially atypical lateralization of the speech and language processes, play an important role in the etiology of stuttering. Various hypotheses suggest that prenatal testosterone causes atypical hemispheric lateralization. The aim of this study was to investigate the role of prenatal testosterone in the etiology of developmental stuttering by the use of the ratio of second- and fourth-digit lengths (2D:4D).