Abstract: What lurks within the crypt? With more than 200 known causes of ischemic stroke (Saver, 2016), what should be the minimum workup? Many centers offer high-resolution brain imaging and vessel studies, telemetry monitoring for atrial fibrillation (AF), trans-thoracic and trans-esophageal echocardiography, and a panoply of laboratory tests. Nevertheless, the proportion of strokes that are cryptogenic still ranges from 10–40% (Saver, 2016) which, problematically, includes not only those with an unknown etiology after diagnostic evaluation, but also those with an incomplete workup, as well as those with multiple possible causes (i.e., ipsilateral carotid stenosis with concurrent AF). Such heterogeneity is suboptimal for clinical practice as well as for research, which intends to generate blanket recommendations.