Background: Midline closure defect malformation (NTD) is a congenital fusional defect of the posterior segments of spinal vertebrae which is associated with high morbidity and mortality. Fetuin-A, Osteopontin, total antioxidant and oxidant levels are unknown in patients with midline closure defects. In this study, the levels of these parameters in patients with NTD and their relationship with the disease were investigated. Methods: The study included 165 patients (0-5 age group) with OHD (Study group, n = 80) and healthy children of similar age (Control group, n = 85). Patients with OHD were divided into three groups as Spina Bifida Occulta (Group I, n = 22), Spinal Meningocele or Myelomeningocele (Group 2, n = 26) and Hydrocephalus (Group 3, n = 31). One-way Kolmogorov-Smirnov test was used to determine whether the distributions were normal or not. Ki-square, student t test, Mann-Whitney U test and Kruskal-Wallis variance tests were used in the comparisons between the groups. Total antioxidant status (TAS) and total oxidant status (TOS) were measured spectrophotometrically. Oxidative stress index (OSI) was calculated with the ratio of TOS to TAS. Results: TAS levels were similar between patient and control groups (p = 0.230). TOS and OSI levels were higher in patients, and fetuin-A and osteopontin values were higher in the control group (for all, p <0.05). TAS levels were similar between patient groups, however, TOS, fetuin-A, osteopontin values were significantly different (p <0.05 for all). The levels of TOS, OSI and Fetuin-A were decreasing steadily from group I to III, whereas osteopontin levels were the highest in the group I and the lowest in the group 2. Conclusion: OHD closure defect occurs during intrauterine period. In the embryogenesis stage, it is a malformation which results in inadequate closure of the midline spinal cord because of inadequate development of neural tissue from the ectodermal layer and because of inadequate development of the bone and skin from the mesodermal layer which surrounding the spinal cord. This insufficient closure can occur anywhere in the neural tube. They require biological and chemical active substances to complete the histogenesis and organogenesis of the neural tube. Therefore, it is thought that TOS, OSI, Fetuin-A and Osteopontin values may play a role during embryological development of OHD patients. [ABSTRACT FROM AUTHOR]