The purpose of this study was to determine the relationship between admission and postoperative platelet count (PC) and mortality and morbidity rates after emergency surgery for ruptured abdominal aortic aneurysm (AAA). We performed a case record review of 65 consecutive patients admitted with ruptured AAA. Five patients did not undergo operation because of poor clinical condition, 12 patients died at operation, 13 patients died after operation, and 35 patients survived (operative mortality rate of 58%). Fifteen patients had an admission PC of less than 150 x 10(9)/L, of whom 14 (93%) died; 27 patients had an admission PC of 150 to 250 x 10(9)/L, of whom 8 (30%) died; and 18 patients had an admission PC of greater than 250 x 10(9)/L of whom 3 (17%) died. At the end of operation 29 patients had a PC of less than 100 x 10(9)/L, of whom 13 (45%) died, 20 (69%) had development of multiorgan failure (MOF), and 6 (21%) required relaparotomy for bleeding complications. By contrast, all 19 patients having a PC of 100 x 10(9)/L or greater at the end of the operation survived, three (16%) had development of MOF, and none required further surgery for bleeding. There was a significant inverse correlation between PC at the end of the operation and the number of postoperative days spent on a ventilator, in the intensive therapy unit, and in hospital. After operation, 15 patients had development of thrombocytosis (PC > 400 x 10(9)/L), of whom 10 had development of deep venous thrombosis and 8 had development of pulmonary embolism. There were no deep venous thromboses or pulmonary embolisms in patients who did not have development of a postoperative thrombocytosis. There is a direct correlation between PC on admission to the hospital and death after emergency repair of ruptured AAA. Thrombocytopenia at the end of the operation is associated with a high risk of morbidity from continuing hemorrhage or MOF. The development of postoperative thrombocytosis is associated with a high risk of thromboembolic complications. PC provides a simple marker of outcome in patients diagnosed with and undergoing operation for ruptured AAA.