Fat embolism is a known complication of marrow infarction in patients with sickle cell disease (Hb S/S and Hb S/C) disease. It should be considered in sickle cell crisis when there is deterioration in respiratory function, a fall in arterial PO2, a normoblastaemia, and a thrombocytopenia in the peripheral blood. We now report a patient in whom the diagnosis was confirmed in life by identifying fat in the sputum, demonstrating disseminated intravascular coagulation, and using a double isotope technique to distinguish recent from old marrow infarction. Use of these features enabled an early diagnosis to be made which led to a successful outcome in a potentially fatal condition.