A 73-year-old male was admitted with right-sided motor weakness and presented with a rare association of incidental venous malformation in the right frontal lobe and a glioblastoma in the left frontal lobe. Computed tomography and magnetic resonance imaging failed to demonstrate typical appearance of venous malformation and showed atypical findings surrounding the suspected vascular lesion. Angiography was needed to obtain the diagnosis of venous malformation. The patient underwent subtotal resection of the glioblastoma and received radiation therapy. The venous malformation was followed up conservatively because it was asymptomatic. Correct diagnosis of coexisting venous malformation is important for the treatment of an associated brain tumor, especially when both lesions are closely located.