Subacute subdural hematoma (SASDH) is a rare entity. We retrospectively reviewed 8 patients with SASDH. Four patients were male and 4 were female, with an age range of 45-87 years (mean, 67.8 years). The minimal level of deterioration ranged from 8 to 14 (mean, 10.5). The deterioration of neurological symptoms was confirmed 4-20 days after injury (mean, 12.9). The hematoma volume was increased in 6 patients. Seven patients underwent surgeries (burr-hole irrigation in 6, craniotomy in 1). The Glasgow Outcome Scale indicated a good recovery in 4 patients and moderate disability in 4 patients. Increased cerebral blood flow was observed just below the SDH in 1 patient. We consider that the hypoperfused tissue in the acute phase might become hyperperfused during the subacute phase owing to impaired autoregulation, and the hyperperfusion may be responsible for the development of the SASDH, leading to deterioration. Further investigations in a larger series are needed to elucidate the mechanism underlying the development of SASDH.