Background: Clinical and computer tomography angiography (CTA) correlates of hyperdense middle cerebral artery sign (HMCAS) and dot sign were revisited in patients treated for acute MCA stroke. Temporal evolution of these signs over 24 hours was assessed quantitatively by density (Hounsfield unit [HU]) measurements. Methods: Maximum pixel-sized HUs throughout proximal MCA and its insular fissure branches were determined in 131 patients with acute MCA stroke treated by intravenous thrombolysis and/or interventional thrombolysis/thrombectomy; 14 patients treated for vertebrobasilar stroke (VBS) and 42 nonstroke control subjects. Utility of visually determined HMCAS and dot sign, absolute HU of proximal and distal MCA, side-to-side HU ratio and difference, and hyperdense MCA burden score for the prediction of early dramatic recovery (EDR) and third-month favorable prognosis were evaluated. The clinical value of the changes in vessel hyperdensity over 24 hours was identified in subjects who received intravenous thrombolysis (99 MCA stoke and 11 VBS). A multivariate model with adjustment for age, baseline stroke severity (National Institutes of Health Stroke Scale [NIHSS]), and CTA-based modified clot burden score (mCBS) was used to determine independent predictors of short-and long-term clinical outcome. Results: The presence of HMCAS and dot sign, their density indices (maximum HU, ipsilateral-to-contralateral HU ratio, and difference), and changes in quantitative attenuation over 24 hours were not significantly associated with EDR and favorable third-month outcome in the multiple regression models, whereas NIHSS and mCBS were found to be significant independent "negative predictors'' of both EDR and favorable prognosis, while age was a strong "negative indicator'' only for 3-month good outcome. Average HU decrease over the first day was 5.7 HU in HMCAS (1) and 2.9 HU in dot sign (1) arteries. The densities of thrombi in MCA and insular branches were not different in subjects with and without cardioembolism. Conclusions: CTA provides dependable (high sensitivity and specificity) information regarding clot size and location, whereas hyperdense artery signs have low sensitivity and just acceptable specificity levels in this regard. However, the prognostic and diagnostic information generated by the presence of hyperdense artery signs and temporal change in attenuation can be useful in acute stroke settings where CTA is not readily available. Quantitative measures, rather than qualitative evaluation have a higher yield in determination of temporal change of the hyperdensity signs and its possible clinical correlates.