Background: Increased concentrations of tumor necrosis factor alpha (TNF-α) in blood and amniotic fluid are observed in women with preterm delivery (PTD) and TNF-α mutations at −308 position are associated with higher expression of this gene. Therefore, we compared the frequency of G308A transition in the promoter region of TNF-α gene of women and neonates delivered preterm with the normal subjects. Methods: This cross-sectional study was performed on 135 mothers who were referred for delivery. According to the gestational age, mothers and their neonates were allocated to the case (preterm, 64 subjects) and control (term, 71 subjects) groups. Using the polymerase chain reaction, restrictive fragment length polymorphism (RFLP), genotyping was performed on both maternal peripheral blood and cord blood samples to determine single nucleotide polymorphism in the promoter region of TNF-α gene at -308. Results: Two mothers in the case group, one mother in the control group and one neonate in the case group had genotyping assays (GA) mutation. All other subjects had normal GG genotype. Frequency of GA mutation was not significantly different between two groups (P = 0.47). Conclusions: There is no significant association between PTD and either maternal or fetal TNF-α −308 polymorphism and frequency ofGAmutation is not significantly increased in mothers and neonates delivered preterm. It means that the presence of this mutation by itself does not modify the overall risk of PTD. Investigations on the combination of various polymorphisms indifferent genes are recommended to achieve more accurate results.