Background: Plasmapheresis is a therapeutic alternative for diseases in which a "humoral factor" has pathogenetic relevance. However it is not devoid of adverse effects. Aim: To review the indications, number of procedures, morbidity and clinical evolution of plasmapheresis in critical patients. Patients and Methods: A retrospective and descriptive study in four intensive care units of an University hospital. The severity of patients was evaluated with APACHE II and SOFA scores. Results: Twenty patients were studied. The most common indications of plasmapheresis were thrombotic thrombocytopenic purpura (TTP) in 50% of subjects and small vessel vasculitides in 30%. The number of procedures per patient oscillated between 2 and 14 (mean: 7.1+/-3.3). The registered adverse effects were hypocalcemia in 50% of patients, hypotension in 42.1%, coagulopathy in 35%, hypokalemia in 29%, rash in 20%, procedure related infections in 18% and fever in 10%. There was a significant decrease of 17+/-28% in prothrombin time, after the procedures. Seventy five percent of patients had a favorable evolution. Global mortality rate was 15%. All deaths occurred in patients with TTP and were attributed to the progression of the disease. No death was attributed to the procedure. The initial APACHE II and SOFA scores were 12.4+/-8.4 and 5.3+/-2.9, respectively. Both scores decreased after the procedure. Among other therapeutic measures, 15% of the patients received immunosuppressant treatment, 27% were dialyzed and 32% were mechanically ventilated. Conclusions: The most common indication of plasmapheresis was TTP. Adverse effects were frequent, however there was no procedure related mortality. The global morality rate was 15% and all deaths occurred in patients in TTP.