Disseminated intravascular coagulation (DIC) is a complication of a variety of severe underlying diseases and a contributing factor in multi-organ failure and death. DIC is diagnosed on the basis of clinical findings (organ failure, bleeding) and laboratory abnormalities. The laboratory data include (repeated) measurements of platelet count and global clotting tests, to which more specific and sensitive tests for activated coagulation are added. The focus of this paper is on thrombocytopenia (platelet count < 100 x 103/microl) as a marker in DIC. First, in patients with suspected DIC it is imperative to consider alternative causes of thrombocytopenia,such as related to heparin use (heparin induced thrombocytopenia II) or thrombocytopenic purpura. Second, the observation of thrombocytopenia in relation to DIC should be interpreted as a marker of advanced or overt DIC and not as an early indicator. According to recommended guidelines measurements of platelet counts should always be coupled to a panel of coagulation markers and not be used as single marker of DIC (or other syndromes). In general, thrombocytopenia should not trigger platelet transfusions except in patients with severe bleeding complications.