The relationship of the lower lip to the maxillary central incisor has been investigated in eighty subjects. Lip posture and incisor angulation were assessed and compared using pretreatment cephalograms of groups of twenty children with Class I, Class II division 1, Class II division 2 and Class III incisor relationships. Results confirm the clinical impression that there is a strong correlation between the class of incisor relationship and lower lip height relative to the upper central incisor. The wide range of lip height in the Class I group, however, indicates that a normal overjet may remain stable in the absence of lower lip cover or, alternatively, in the presence of a high lip line. The stability of upper incisor position depends upon the absence of unbalanced forces and lower lip cover is only one factor.