The objectives of this study were to quantitatively evaluate the relationship between frontal craniofacial morphology and the horizontal balance of the lip-closing forces (LCF) generated during maximum voluntary pursing-like movements in patients with mandibular deviation. Thirty-one subjects (median age 25·4 ± 8·9 years) without a history of orthodontic treatment were randomly selected from among the orthodontic patients who visited our hospital. Lip-closing forces was recorded in eight directions during maximum voluntary pursing-like lip-closing movements. The subjects were divided into the deviation (two males and 11 females) and non-deviation groups (four males and 14 females). There was no significant difference in the total LCF between the deviation and non-deviation groups. In the deviation group, the mean LCF value on the deviation side of the upper lip was significantly lower than that detected on the non-deviation side of the upper lip, while the mean LCF value for the deviation side of the lower lip was significantly higher than that for the non-deviation side of the lower lip. In contrast, no significant difference in upper or lower lip LCF was detected between the deviation and non-deviation sides in the non-deviation group. The difference in the LCF generated in the lower lip between the deviation and non-deviation sides was significantly positively correlated with mandibular menton deviation and significantly negatively correlated with the difference in maxillary height between the deviation and non-deviation sides. These results suggest that the horizontal balance of the upper and lower lip LCF produced during pursing-like lip-closing movements in patients with mandibular deviation is related to frontal craniofacial morphology.