T2*-weighted gradient-echo (GE) magnetic resonance images frequently demonstrate small hypointense lesions in patients with systemic hypertension and spontaneous hematomas. These lesions have been suspected to represent subclinical microhemorrhages. We examined the incidence of these lesions in neurologically healthy adults, and the factors associated with them. Axial T2*-weighted GE images (TR = 1,000 ms, TE = 30 ms, flip angle = 20 degrees) were obtained in addition to conventional T1- and T2-weighted spin echo images in 450 neurologically healthy Japanese adults (289 men and 161 women; age 52.9 +/- 7.7 years, range 24-84). The overall incidence of small hypointense lesions was 3.1% (14/450), and these lesions were closely related to systemic hypertension (P < 0.0001) and heavy cigarette smoking (>20 cigarettes per day; P=0.003). Although the incidence of hypointense lesions was lower in neurologically healthy adults than in the reported incidence in patients with a hemorrhagic history, the presence of these lesions was related to the risk factors for primary intracerebral hemorrhage even in the neurologically healthy adults.