Based on reports in the literature on the success and low morbidity of twist drill craniostomy (TDC) and closed system drainage (CSD) for chronic subdural hematomas, a prospective study was initiated in 1981 and included all symptomatic patients presenting with a history and clinical and computed tomographic (CT) findings consistent with subacute or chronic subdural hematoma. A total of nine patients were treated with TDC and CSD as the initial procedure. An asymptomatic or progressively improving patient with greater than 50% reduction in subdural size by repeat CT scan was set as the end point of therapy. There were no complications, all patients improved with drainage, and seven were cured by this method alone. The results are compared retrospectively to surgically treated patients, and an overall decrease in morbidity and length of hospitalization are noted. The technique and CT scan correlations are described, and the rationale for use of this method is discussed in terms of our current understanding of the pathophysiology and complications of the disease.