We retrospectively analyzed 20 lesions of occult cerebral vascular malformation (OCVM) examined by CT, angiography and high-field (2.0T) MR in 14 patients. All lesions were angiographically occult. Diagnosis was based on the typical clinical history and characteristic radiologic findings in all patients and confirmed by surgery in 3 patients. MR demonstrated all lesions as hemorrhagic foci. The most common and typical MR finding of OCVM was circumscribed thick hypointense rim on T2-weighted images (T2-Wls) representing hemosiderin deposit with various central intensities suggesting the presence of hematomas in different stages (11 lesions). Among these, the recurrent hemorrhage in small amount produced the characteristic "a bunch of grape" appearance. But, small OCVM less than 1 em in diameter was identified as a small homogeneous hypointense nodule on T2-Wls with sharp (6 lesions) or fade-out (1 lesion) border. There were 2 lesions showing atypical findings such as dense hemosiderin rim with central lacuna or bilobed subacute hematoma. As the associated MR findings which strongly suggest the diagnosis of OCVM signal void due to feeding or draining vessels was found in 4, lesions and the surrounding focal cortical atrophy or leukomalacia in 2 lesions. The predilection site of OCVM was subcortical (8 lesions) and periventricular (6 lesions) location. CT depicted 16 of the 20 lesions, but missed 4 lesions of small OCVM. CT alone did not permit definitive diagnosis of OCVM in most cases. Fifteen lesions demonstrated on CT contained somewhat hyperdense area in central or peripheral location Peripheral hyperdense area corresponded to the dense hemosiderin deposit on MR and central one to the hematoma formed by recent hemorrhage. Low density area on CT usually corresponded to liquefif.1 subacute hematoma on MR.