The purpose of this study was to review the incidence of extreme thrombocytosis (ExT) (platelet count 1,000,000/microL or greater) in trauma patients and to examine the role of antiplatelet agents in its treatment. The Los Angeles County Medical Center trauma registry was used to obtain injury demographics, medications, and daily platelet counts for injured patients 16 years of age or older admitted between July 2005 and February 2008. Of 6,985 total trauma patients admitted during the study period, 95 developed ExT (1.4%). Average age was 29 years (range, 16-63 years), 89 per cent were male, 44 per cent had penetrating trauma, and mean Injury Severity Score was 24 (range, 1-57). Of the 95 patients with ExT, 41 were treated with aspirin (43%) and 54 were not (57%). The two groups did not differ with regard to basic demographics, injury patterns, vitals on admission, or splenectomy rate (34 vs 20%, P = 0.13). After adjusting for maximum platelet counts and duration of ExT, there was no difference between the treated and untreated groups in terms of mortality, complications, and intensive care unit or hospital lengths of stay. The incidence of ExT is approximately 1.4 per cent in trauma patients. Antiplatelet therapy does not affect ExT patient outcome. Further prospective studies are warranted.