1. "Thrombotic thrombocytopenic purpura" is the name which we propose for a rare but well-defined disorder which manifests itself clinically as an acute febrile illness and which is characterized by (a) petechiae and ecchymoses, thrombocytopenia, prolonged bleeding time and poor clot retraction, (b) by a severe anemia out of proportion to any observed blood loss, (c) by mild acholuric jaundice, hepato-splenomegaly, (d) by bizarre and intermittent mental and neurologic symptoms and signs, and (e) by a transient leukemoid reaction in the peripheral blood.

2. This clinical picture must be correlated with a remarkable histologic pattern, namely the presence of myriads of platelet thrombi in the small arterioles and capillaries of almost all organs of the body.

3. Eleven such cases have been described in the literature. One case of our own is added.

4. The clinical features of this disease are detailed and the differential diagnosis is discussed. It is emphasized that if the physician is familiar with this syndrome a correct clinical diagnosis may become readily possible.

Acknowledgment for the support of this work is made to the Hulda B. and Maurice L. Rothschild Foundation for Scientific Research.