Paradoxical reactions (Jarish Herxheimer-like reactions) have been described in patients treated with praziquantel (PZQ) during acute schistosomiasis (infected >/= 3 mo), while PZQ treatment of chronic schistosomiasis is generally considered to be safe. We report an acute febrile reaction with respiratory decompensation following PZQ treatment in a 17-year-old male patient who had no potential (re)exposure to infection for at least 5 months and was therefore considered to have reached the chronic stage of disease. We speculate that the clinical manifestations in our patient constitute a very late paradoxical reaction in an unusually long acute phase of infection