Clinical trials of bithionol in treating Paragonimus westermani lung infection have been conducted in areas of endemic infection. Bithionol has been reported to cure over 90% of infected patients. We report a case of a 32-year-old Laotian man residing in Connecticut who relapsed with P. westermani pneumonitis 4 months after apparent eradication of infection with bithionol (40 mg/kg by mouth every other day for 10 doses). He was successfully treated with a second course of bithionol (40 mg/kg by mouth every other day for 15 doses). The mechanism of relapse of P. westermani infection following bithionol therapy should be evaluated.