In view of the large number of pregnancies complicated by neural tube defect (NTD) in Khuzestan, south west Iran, this study assesses the prevalence of NTD and its ecological and social factors. Methods: This is a retrospective study, based on medical documents using an analytic assessment of NTDs in pregnant women attending the Jundi Shapur University hospitals in Ahvaz from 2 March 2002 to 20 March 2004. Results: The total number of pregnant women was 3,262 and 56 pregnancies were complicated with NTD. A large number of the infants with NTDs were female (70%) and the most common anomaly was anencephaly. The prevalence was 4.2 in ,000 births. The percentage in primigravida was 42.6% and in multigravida 57.4%. The main risk factor for NTD was age of the mother, those between 2 and 30 being the most affected. Consanguinity is the second risk factor with 3% of cou ples who were close relatives. Other socio-demographic factors were also significant. Conclusion: This retrospective study confirms clinical observation that pregnancies complicated by NTD in Khuzestan are common. There are various ecological and social factors that correlate with the prevalence of NTD.