Thrombocytopenia is the most common haemostatic disorder in patients admitted to Intensive Care Units (ICUs). The mechanisms contributing to a decrease in the platelet count in critically ill patients are multifactorial, among which sepsis and trauma are the most frequent. A differential diagnosis of profound thrombocytopenia is crucial for effective treatment. A low platelet count is a strong independent predictor of morbidity and mortality because it is associated with life-threatening bleeding or thrombosis. This article aims to outline the definition and pathophysiology of thrombocytopenia and present a three-step algorithm of the clinical management of this haemostatic disorder.