Background and Purpose-The aim of the study was to investigate the utility of iodine contrast agent leakage (the iodine sign) analyzed by Gemstone spectral imaging in early hematoma formation compared with that of the spot sign for predicting early hematoma expansion (HE) and poor functional outcomes. Methods-From 2014 to 2017, 91 patients with spontaneous intracerebral hemorrhage who underwent spectral computed tomography angiography within 6 hours of spontaneous intracerebral hemorrhage onset were prospectively included in our study. We defined a positive iodine sign as tiny enhancing foci within the hematoma on Gemstone spectral imaging and an iodine concentration inside the foci of >7.82 (100 mu g/mL). Univariate and multivariate logistical regression analyses were performed to assess risk factors for HE, and the predictive value of HE was analyzed. Results-Positive spot and iodine signs were present in 38.5% (35/91) and 57.1% (52/91) of the patients, respectively. Using multivariate analysis, the iodine sign independently predicted HE (odds ratio, 53.67; 95% CI, 11.88-242.42; P<0.001) and had a higher sensitivity (91.5% versus 63.8%), negative predictive value (89.7% versus 69.9%), and accuracy (85.7% versus 75.8%) for detecting HE than the spot sign. The iodine sign, but not the spot sign, was significantly related to poor functional outcomes (severely disabled and vegetative state) in all patients (chi(2)=29.97; P<0.001). Conclusions-The iodine sign is a reliable and sensitive marker for predicting HE and poor functional outcomes.