Blastocystis hominis (B. hominis) is a cosmopolitan pro- tozoa which parasitizes the human large intestine. This parasite had been considered to be commensal of the large intestine for a long time, because even an intense invasion may be asymptomatic. However, this species is now being regarded as a parasitic organism. In this paper the latest data concerning the epidemiology, diagnostics and treatment of B. hominis invasion have been cited and discussed.