Background/Purpose: Previous studies have shown that the develop-ment of the first permanent mandibular molar (M1inf.) is deviant in children with unilateral cleft lip and palate (UCCLP) and in children with isolated cleft palate (CP). Also, a significant correlation between severity of CP and delay of M1inf. maturation was found. The aim of the present study was to test if similar deviations are present in children with Bilateral Complete Cleft Lip and Palate (BCCLP). The following hypotheses were tested: (1) M1inf. is not delayed in maturation in children with BCCLP. (2) M1inf. has normal size in children with BCCLP. Methods/Description: Study group: A consecutive sample consisting of 19 children with BCCLP at 2 and 22 months. Control group: A consecutive sample of 44 children with Unilateral Incomplete Cleft Lip (UICL) at 2 and 22 months of age. In lateral cephalometric X-rays follicle maturation (FM) was assessed according to Haavikko at 2 and 22 months of age. The width of the M1inf. follicle (FW) was measured at 2 and 22 months of age. The width of the crown (CW) was measured at 22 months of age. Intra-rater reliability was determined by duplicate measurements in 30 subjects. The relationship between stage of mineralization in BCCLP and controls was tested using a Mantel-Haenszel test. Pearson's correlation coefficient R was used to describe the relationship between FW and FM. Differences between group means of FW as well as of CW were tested using Student's t-test. Level of significance: 5%. Results: Intra-rater errors: FM kappa = 0.87 (excellent agreement); FW and CW coefficient of variation=1.8%; Dahlberg's s(i)=0.2 mm. FM was significantly delayed in BCCLP at both 2 (p