Computed tomography (CT) findings of chronic subdural hematomas are usually diagnostic, unless hematomas are isodense and bilateral. The authors report two cases of bilateral chronic subdural hematomas, in which CT scans on admission were both misdiagnosed as delayed subarachnoid hemorrhage (SAH). The first case was a 43-year-old woman who suffered from a sudden onset of headache and nausea. She had no past history of head injury. CT scans on admission did not clearly reveal the Sylvian fissures and the mesencephalic cistern, without any mass effects. A lumbar puncture demonstrated xanthochromic cerebrospinal fluid (CSF), which was considered to be responsible for her headache. Cerebral angiography performed on day 4 failed to demonstrate any cerebral vascular disorders. Follow-up CT scans on day 7 demonstrated a high density lesion in the left subdural space. Magnetic resonance images (MRIs) confirmed a diagnosis of bilateral chronic subdural hematomas. Removal of the hematomas cleared all signs and symptoms smoothly. The second case was a 44-year-old man who was referred from another hospital because of xanthochromic CSF found by lumbar puncture. He began to suffer headache and be subject to vomiting 6 weeks earlier and these symptoms were still present on the day of admission. CT scans did not clearly show the cerebral cisterns without mass effects. Because the second lumbar puncture showed xanthochromic CSF again, SAH from aneurysm was suspected. However, emergency cerebral angiography failed to demonstrate cerebral aneurysms. MRI performed two days later demonstrated bilateral chronic subdural hematomas. Following surgery, the patient improved immediately and was discharged from hospital without any complications. In both cases, a retrospective study of the angiograms revealed the evidence of bilateral avascular areas over the convexities in the venous phase. The reason why these subdural hematomas were missed at the time of angiography was due to too much attention being paid to the arterial phase in an effort aimed only at identifying cerebral aneurysms. There are no reports of chronic subdural hematoma which demonstrated sudden onset of headache associated with xanthochromic CSF.