Schistosoma mekongi, a parasite of the dog which is endemic in small foci along the Mikong river, is rarely seen in Europe. A case of schistosomiasis caused by S mekongi was recently seen in France, in a native of Laos who had been living in Thailand. He was admitted for treatment of previous diagnosed tuberculoid leprosy but was found to have hepatosplenomegaly, with a high eosinophil count and high bilirubin concentrations. Serological examination suggested schistosomiasis, but there were no parasites in the urine and the rectal mucosa looked normal on endoscopy. Nevertheless, rectal biopsy showed schistosomal proctitis and many ova of S mekongi. Two courses of praziquantel cleared the ova from his rectal mucosa. Although serological examination using S mansoni antigen suggested schistosomiasis, only biopsy of normal looking rectal mucosa allowed the diagnosis to established.