A study of 1016 12-year-old Nigerian children was carried out to assess the relationship between traumatic injuries of anterior teeth, incisor overjet and lip competence. The prevalence of dental injuries was 10.9% which confirmed the results of previous studies. More boys than girls sustained injuries to their teeth. There were, however, no significant sex differences in increased overjet or lip competence. Of the 111 children with traumatic dental injuries, 71 (64.0%) had increased incisor overjet (> 3 mm) compared to 257 of the 905 children (28.4%) in the non-trauma group. Similarly, 72 (64.9%) of the trauma group had inadequate lip coverage compared to 224 (24.8%) in the non-trauma group. These differences were statistically significant (P < 0.001). It is concluded that incisor overjet of more than 3 mm and incompetent lips are significant predisposing factors to anterior dental injury in Nigerian children.