Background: Patients with intracerebral hemorrhage (ICH) often report the use of antiplatelet medications, even more commonly than the use of anticoagulants. The effect of antiplatelet drugs on the course of ICH is controversial. In this study, our aim was to determine the effects of previous antiplatelet therapy on admission hematoma volume and hematoma expansion in patients with spontaneous ICH. Methods: A consecutive series of patients with a diagnosis of ICH who underwent brain computed tomographic (CT) scans within 12 hours of symptom onset and a follow-up CT scan within 72 hours were included in the study. Hematoma volume was calculated by using the ABC/2 method on admission and follow-up images. Univariate and multivariate analyses were performed to determine the independent role of antiplatelet use on baseline hematoma volume and hematoma expansion (defined as an increase in hematoma volume >12.5 mL or 33% of the baseline ICH volume). Results: A total of 153 patients were included in the study. Fifty-two (34%) patients were using antiplatelet drugs at the time of symptom onset. Antiplatelet users tend to have a larger baseline hematoma volume; however, this difference failed to reach statistical significance (P=.17). Antiplatelet therapy was found to be a significant determinant of substantial hematoma expansion, both in univariate and multivariate analyses (P<.01). Conclusions: Previous antiplatelet use significantly contributes to hematoma expansion in patients with ICH.