The change in size of a ruptured anterior cerebral artery aneurysm was recorded in a series of angiograms. The aneurysm did not appear on the initial angiogram, but was seen on the second study. Incomplete filling was seen on the third angiogram, and the aneurysm appeared to have thrombosed on the fourth angiogram. On the fifth angiogram, done 5 weeks after the first, the aneurysm filled completely. It was subsequently clipped.