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Recent advances in time-sensitive mechanical thrombectomy for the treatment of emergent large vessel occlusion (ELVO) have changed the role of prehospital providers from simply identifying a stroke to identifying the likely presence of ELVO. No one method for identifying ELVO in the field has been demonstrated to be superior. We sought to describe how this might be best accomplished using the Los Angeles Motor Scale (LAMS) in concert with other physical exam findings by paramedics and emergency medical technicians (EMTs). We had paramedics and EMTs examine patients with suspected stroke in the hospital. We compared their exams to the standard neurologist exams and to the results of angiography. We performed multiple analyses to identify the exam elements that would best identify large vessel occlusions. Using LAMS with a threshold score of 4, sensitivity for stroke and ELVO, respectively, was 27% (95% CI 20-36%) and 42% (95% CI 30-55%). When a LAMS of 3 was used in concert with speech abnormality, sensitivity improved to 36% (95% CI 28-45%) and 61% (95% CI 48-73%). Specificity of this model was 70%, (95% CI 64-75%). Most striking was the negative predictive value of this model for ELVO: 90% (95% CI 85-93%) The LAMS or LAMS plus speech can be used to decrease the number of missed large vessel occlusions and to route suspected large vessel occlusions to thrombectomy-capable centers. Other, more complicated scales may have little additional benefit. This derivation data set is the first to use paramedics and EMTs as examiners prospectively and supports prehospital protocol change underway in New York City.