Our aim was to investigate the differences in the dynamics of lip force between a group of participants with repaired cleft lips and a group of patients the same age but without clefts. We evaluated 101 children between the ages of 10 to 15 years (unilateral clefts n = 35, bilateral clefts n = 15, class I malocclusion n = 25, and class III malocclusion n = 26). Maximum and minimum forces required to close the lips were evaluated with the Lip De Cum (R) device (Cosmos Instruments Co Ltd, Tokyo, Japan) for the all groups. We found no significant differences between the maximum and minimum values between boys and girls within the groups, whereas the mean maximum and minimum lip force of the boys was higher than those of the girls in all the groups. This study showed that maximum and minimum lip closing force values were statistically similar in all groups. We conclude, therefore, that patients with bilateral cleft lip have reduced maximum and minimum lip force. (C) 2017 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.