International Journal of Paediatric Dentistry 2012; 22: 280-285 Background. Based on measurements on dental casts, smaller permanent teeth in children with cleft palate have previously been reported in the literature; however, the early maturation of teeth and the size of the follicles and crowns have not been investigated. Hypothesis. The maturation of the mandibular permanent first molar (M1(inf) ) is delayed, and the mesiodistal diameters of the follicle and crown of M1(inf) , respectively, are reduced in children with isolated cleft palate (ICP). Design. Retrospective, longitudinal. Cephalometric X-rays were available for 2 and 22 months old children with clefts (64 children with ICP, and a control group of 38 children with unilateral incomplete cleft lip). The width of the follicle and the crown of M1(inf) , and the maturation of M1(inf) were assessed. Intra-observer error was acceptable. Results. M1(inf) maturation was delayed in children with ICP at both 2 and 22 months of age. The mesiodistal diameter of the crown of M1(inf) in the ICP group was reduced. Thus, the two hypotheses could not be refuted. Conclusions. Children with ICP showed smaller dimensions of the M1(inf) , and in addition, the maturation of M1(inf) was delayed.