The purpose of this study was to investigate the prevalence of neurodevelopmental delay among deformational plagiocephaly (DP) children, and to confirm relationship between neurodevelopmental delay and severity of DP.This study is retrospective study. Five hundred thirteen children who visited for abnormal head shape through outpatient department were recruited. To identify the children with neurodevelopmental delay among the 513 children with DP, Denver Development Screening Test (DDST) was performed in 38 children who suspected of neurodevelopmental delay. Cranial vault asymmetry (CVA) was measured by using caliper, and cranial vault asymmetry index (CVAI) was calculated. Thirty eight children with DP who conducted DDST were divided into 2 groups according to the degree of CVA; group 1 included 21 children with CVA under 10 mm, and group 2 included 17 children with CVA over 10 mm.There was a significant difference in number of neurodevelopmental delay between group 1 (n = 7) and group 2 (n = 14) (P < .05). Mean grade of DP, CVA, and CVAI (1.76 ± 0.44, 5.90 ± 2.21 mm, 4.20 ± 1.51%) in group 1 was smaller than that in group 2 (3.41 ± 0.8, 12.71 ± 3.22 mm, 8.83 ± 2.18%), respectively (P < .05).Our results found that the frequency of developmental delay was significantly increased in children with CVA more than 10 mm. Doctors who take care of children with DP had better keep developmental delays in mild.