Among 380 bone marrow transplant (BMT) recipients, five cases (1.3%) of clonorchiasis were observed from 1991 to 1996. Clonorchis sinensis infection was evident in the results of stool examinations performed for screening purposes 7 days before bone marrow transplantation. Salmonella species were isolated concomitantly from the stools of two of the five patients. None of the patients had symptoms due to clonorchiasis. Ultrasonography did not show dilated hepatobiliary ducts, stones, or periportal fibrosis. Fatty liver changes were detected in one patient. All five patients received praziquantel (25 mg/kg po t.i.d. for 1 day) before bone marrow transplantation. Only two patients who underwent allogeneic transplantation had mild venoocclusive disease of the liver with transient hyperbilirubinemia and mildly elevated liver enzyme levels, whereas hyperbilirubinemia or elevated serum alanine aminotransferase levels, related to conditioning toxicity, occurred in two other patients. After treatment with praziquantel, stool examination for all five patients were negative for C. sinensis ova. In addition, Salmonella species were not detected after ciprofloxacin prophylaxis. All five patients survived for > 300 days. Given the availability of effective therapy and in the absence of excessive complications, clonorchiasis is not a contraindication to bone marrow transplantation.