It has been customary to designate crescent-shaped subdural hematomas at angiography as "acute" and biconvex hematomas as "chronic." Analysis of angiograms in 57 proven cases of subdural hematoma reveals that: (1) only 14 per cent of subdural hematomas have a biconvex shape; (2) crescent-shaped hematomas occur at any time interval after injury; and (3) biconvex hematomas may occur any time after 11 days. We conclude that there is no valid basis for predicting the age of a subdural hematoma from its configuration at angiography. Since the shapes of the hematomas at angiography do not correlate with the clinical stages of subdural hematoma, the terms "acute" and "chronic" are best not employed in the radiologic description. The preponderance of biconvex hematomas in the older age group suggests that cerebral atrophy may play a role in determining the shape of a subdural hematoma.