Introduction: Pneumocystis jirovecii is one of the most important opportunistic pathogens affecting AIDS individuals and immunodepressive patients. In spite of the fact that it was observed one hundred years ago for the first time, many fundamental aspects of its biology and the morbidity it causes are still unknown.
Objective: this paper was aimed at presenting updating on the main aspects of the history, the epidemiology and the biology of P. jirovecii and the disease it causes.
Conclusions: a number of review articles have been published since the discovery, all of which provide details and novel elements of the microorganism. However, few original papers dealing with this problem have been found in the Spanish literature.