Background and Purpose-Early CT signs of cerebral ischemia are subtle. Little is known of which factors influence the detection of infarct signs. We compared neuroradiologists’ scan readings with those of other specialists involved in the care of stroke patients. Methods-We used the Internet to show 63 CT scans, all acquired < 6 hours after stroke and representing different patient ages, times to scanning, stroke severity, and early CT signs of ischemia to physicians involved in stroke care. They completed a structured scan interpretation proforma over the Internet. We compared the detection of early ischemic signs stratified by severity and the effect of prior stroke between different specialties. Results-Among 207 observers, neuroradiologists saw significantly more of "any early ischemic changes" than did stroke physicians, general radiologists, geriatricians, or neurologists (all P < 0.0001), predominantly due to neuroradiologists' greater detection of "mild" hypoattenuation or swelling. Detection of "severe" hypoattenuation or swelling, and hyperattenuated arteries did not differ between specialties. Old infarcts impaired recognition of early ischemic signs. Nonneuroradiologists did not "overcall" signs. Years of scan-reading experience did not account for these differences, but neuroradiologists took, on average, 30 seconds longer to read each scan than did most other specialists (P < 0.0001). Conclusions-Nonneuroradiologists should realize that they are unlikely to overcall signs, that old infarcts may distract them from seeing early ischemic signs, and read stroke CT scans more slowly, as these factors may help them perform more like neuroradiologists.