We evaluated a method for quantifying vasogenic edema (VE) on MRI to identify brain hematomas caused by neoplasms. We performed a blinded review of 68 acute and subacute hematomas caused by neoplasms (22), hypertension or presumed amyloid angiopathy (27), or vascular malformations (19). The extent of vasogenic edema was quantified on an axial T2-weighted image using the VE ratio: the maximum width of high signal surrounding a hematoma and the mean diameter of the hematoma. Hematomas caused by neoplasm were associated with more vasogenic edema (mean VE ratio 104%+/-15%; mean VE width 2.4+/-0.7 cm) than non-neoplastic hematomas (mean VE ratio 37%+/-5%; P =0.001). When the width of VE was equal to or more half the diameter the hematoma (VE ratio 50%), the positive predictive value for tumor was 66%; when it was equal to or more than the diameter, the positive predictive value was 71%. All six hematomas with VE ratios > or = 150% were caused by neoplasm.