High precision is optimal in prehospital diagnostic algorithms for strokes and large vessel occlusions (LVOs). We hypothesized that prehospital diagnostic algorithms for strokes and their subcategories using machine learning could have high predictive value. Consecutive adult patients with suspected stroke as per emergency medical service personnel were enrolled in a prospective multicenter observational study in 12 hospitals in Japan. Five diagnostic algorithms using machine learning, including logistic regression, random forest, support vector machine, and eXtreme Gradient Boosting (XGBoost), were evaluated for stroke and subcategories including acute ischemic stroke (AIS) with/without LVO, intracranial hemorrhage (ICH), and subarachnoid hemorrhage (SAH). Of the 1446 patients in the analysis, 1156 (80%) were randomly included in the training cohort and 290 (20%) were included in the test cohort. In the diagnostic algorithms for strokes using XGBoost had the highest diagnostic value (test data, area under the receiver operating curve [AUROC] 0.980, confidence interval [CI; 0.962–0.994]). In the diagnostic algorithms for the subcategories using XGBoost had a high predictive value (test data, AUROC [CI], AIS with LVO 0.898 [0.848–0.939], AIS without LVO 0.882 [0.836–0.923], ICH 0.866 [0.817–0.911], SAH 0.926 [0.874–0.971]). Prehospital diagnostic algorithms using machine learning had high predictive value for strokes and their subcategories.