Purpose: In this study, we aimed to determine the incidance, causes, clinical outcomes and the effect on mortality and morbidity of thrombocytopenia in an University internal medicine intensive care unit (IMICU). Materials and Methods: Between July 2011 and August 2012, 165 patients who were followed up in intensive care unit and whose platelet count was below 150,000 / uL were included in the study. The causes of thrombocytopenia were investigated. Patients with and without thrombocytopenia were compared in terms of mortality and duration of stay in intensive care unit. Results: During the study period, thrombocytopenia was developed in %30.1 of patients in IMICU (165/548). Causes of thrombocytopenia in 30 (% 18) patients was sepsis and in 18 (% 10,9) was disseminated intravascular coagulation (DIC).. During the study, 115 (% 69.7) of 165 thrombocytopenic patients and 173 (% 45.1) of 383 non-thrombocytopenic patients died. Mortality in the patients with thrombocytopenia was higher. There was a statistically significant increase in mortality as the platelet count drops. Statistically significant increase in mortality were detected as the platelet count decreased in patients with the same APACHE II score. Conclusio: The most common causes of thrombocytopenia are sepsis and DIC, and thrombocytopenia is an effect that increases the mortality in the intensive care unit.