Monosomy 18p syndrome is caused by partial deletion of the short arm of chromosome 18. Monosomy 18p is an autosomal deletion syndrome. Since the first report of monosomy 18p in 1963, more than 150 cases have been reported. We describe a 2-month-old boy who had monosomy 18p with bilateral cleft lip and palate. Chromosome analysis showed that the karyotype was 45,XY,der （18;21） （q10;q10）. At 5 months 1 year of age, cheiloplasty was performed. At 3 years of age, palatoplasty was performed. Further follow-up will be continued to check his development, including maxillofacial growth.