Background: Delays in the prehospital phase jeopardize the chances for stroke patients to be treated with thrombolysis. However, the causes of prehospital delay remain obscure. We assessed the causes of prehospital delay among patients with acute ischemic stroke. Methods: In this prospective cohort study, we included patients admitted to the Stroke Center of the University Hospital Basel, Switzerland, with an acute ischemic stroke. A corresponding positive Diffusion Weighted Imaging MR was required to be included in the study, i.e. patients with no or negative DWI-MR were excluded. Trained study nurses interviewed all patients or their proxies in person at the bedside. The study period spanned from September, 2015 to July, 2017. Results: Overall, 321 patients were included. The median NIHSS score was 3 (interquartile range [IQR]: 1-5). Median delay between symptom onset and call for help was 55 minutes (IQR: 10-420). The mode of transportation to the Stroke Center was with paramedics (ambulance or helicopter) for 60 % of patients, without in 40% (private car: n=72; taxi: n=31; public transportation, walk-in or other: n=25). NIHSS was higher in patients transported with paramedics (4 [IQR 2-6] vs. 1.5 [0-3], P <0.001). A family physician was consulted immediately prior to hospitalization by 11% of patients (n=35), 89% were admitted directly to the hospital, and the difference in NIHSS was not statistically significant. The thrombolysis ratio was 25%. After adjusting for NIHSS, the odds of thrombolysis were higher among patients transported with paramedics (adjusted odds ratio [aOR]: 2.4, 95%-CI: 1.2-4.7, P=0.01), and lower among patients with prior family physician consultation (aOR: 0.10, 95%-CI: 0.01-0.77, P =0.03). Conclusions: One out four patients wait 7 hours or more before calling for help, a considerable delay. Transport with paramedics was associated with increased chances of thrombolysis. One in ten patients consulted a family physician immediately prior to hospitalization, reducing by 90 percent points the chances of thrombolysis. Identifying and informing family physicians who see patients with symptoms of an acute stroke may be a so far underestimated, cost-effective measure to increase the rate of thrombolysis.