Pneumocystis was first described in 1909 as an evolutionary phase in the life cycle of Trypanosoma cruzi by Chagas [1]. Later it was defined as a different organism [2]. Pneumocystis pathogenesis in humans was shown in 1951 for the fist time [3]. Recently, a species of Pneumocystis which afflicts humans was named Pneumocystis jiroveci [4].