Background and Purpose— The presence of active contrast extravasation (the spot sign) on computed tomography (CT) angiography has been recognized as a predictor of hematoma expansion in patients with intracerebral hemorrhage. We aim to systematically characterize the spot sign to identify features that are most predictive of hematoma expansion and construct a spot sign scoring system. Methods— We retrospectively reviewed CT angiograms performed in all patients who presented to our emergency department over a 9-year period with primary intracerebral hemorrhage and had a follow-up noncontrast head CT within 48 hours of the baseline CT angiogram. Three neuroradiologists reviewed the CT angiograms and determined the presence and characteristics of spot signs according to strict radiological criteria. Baseline and follow-up intracerebral hemorrhage volumes were determined by computer-assisted volumetric analysis. Results— We identified spot signs in 71 of 367 CT angiograms (19%), 6 of which were delayed spot signs (8%). The presence of any spot sign increased the risk of significant hematoma expansion (69%, OR=92, P <0.0001). Among the spot sign characteristics examined, the presence of ≥3 spot signs, a maximum axial dimension ≥5 mm, and maximum attenuation ≥180 Hounsfield units were independent predictors of significant hematoma expansion, and these were subsequently used to construct the spot sign score. In multivariate analysis, the spot sign score was the strongest predictor of significant hematoma expansion, independent of time from ictus to CT angiogram evaluation. Conclusion— The spot sign score predicts significant hematoma expansion in primary intracerebral hemorrhage. If validated in other data sets, it could be used to select patients for early hemostatic therapy.