OBJECTIVE: The authors investigated the role of transcranial Doppler ultrasound (TCD) in clinical decision making about vasospasm due to subarachnoid hemorrhage (SAH). METHODS: In this retrospective study, a total of 383 patients, admitted to our hospital between January 2001 to December 2004 and treated surgically with the diagnosis of aneurysmal SAH, were examined by TCD. RESULTS: Blood flow velocity (BFV) was significantly lower in older patients than in younger patients (p<0.01). BFV in the hypertensive patients were not significantly lower than in the normotensive individuals (p=0.93). The amount of blood clots in the computed tomography after SAH was significantly correlated with BFV (p<0.01). However, there was no statistically significant difference between Hunt-Hess Grade and BFV (p=0.54). The maximum mean flow velocity was greater in 54 patients who developed a delayed ischemic neurological deficit(DIND, 144.1 cm/sec) than in 221 patients who did not develop DIND (94.3 cm/sec, p=0.04). A maximum velocity increase of 40.6 cm/sec/24hr was recorded higher in patients with DIND, compared to that of 22.6 cm/sec/24 hr in patients without DIND (p<0.01). Lindegaard's index (LI) was higher in patients with DIND (4.6) than in those without DIND (2.8, p<0.01). Peak velocity, maximum velocity increase, and LI can thus assist in diagnosis of DIND, however, when those readings made before onset of DIND were considered, there was only significant difference in LI between the groups. CONCLUSION: Serial TCD studies after SAH are of value to detect cerebral vasospasm, especially, LI is significantly correlated with identifying patients who later develop DIND.