OBJECTIVE: To show a high frequency of human mitochondrial DNA (mtDNA) D-loop variations present in infertile women undergoing in vitro fertilization-embryo transfer (IVF-ET) and the variation's potential relevance as a predictive marker in the IVF-ET. STUDY DESIGN: The entire mtDNA D-loop region was amplified in 3 overlapping polymerase chain reaction fragments, and the variations were evaluated through direct DNA sequencing methods in 156 infertile women undergoing IVF-ET. RESULTS: A total of 48 variations were found at 47 positions in the D-loop of all patients. The incidence of variations (particularly 16191 C -> T [p=0.032], 16519 T -> C [p=0.043], 326 A -> G [p = 0.003], and 432 A -> C [p = 0.042]) was significantly higher in patients with top quality embryo rate <= 41.84% (p = 0.004). However, variations were not significantly associated with the fertilization rate (p = 0.846), cleavage rate (p = 1.000), pregnancy rate (p = 0.839), implantation rate (p = 0.911), or miscarriage rate (p = 0.658). CONCLUSION: Our data suggest that the increase in mtDNA variations in the peripheral blood from infertile women could have a predictive value for the outcomes of infertile women undergoing IVF-ET.