['To describe a parasitic infection that probably affected the implantation of good-quality embryos in an in vitro fertilization (IVF) cycle.', 'Case report.', 'Tertiary care center in a university hospital.', 'A 36-year-old Caucasian female with primary unexplained infertility. The patient underwent two cycles of IVF with good-quality embryos transferred; however, no pregnancy ensued despite adequate luteal support.', 'In vitro fertilization cycles, CBC, blood smear, evaluation for eosinophilia including serological evaluation for parasitic infections.', 'Pregnancy.', 'Following treatment for filariasis, a repeat IVF cycle using the same stimulation protocol yielded a full-term pregnancy.'] Is filariasis infection a probable cause of implantation failure in in vitro fertilization cycles?