The advent of thrombolysis has offered a remarkable opportunity for treatment of acute ischemic stroke. Other therapies involving neuro-protection may be forthcoming. These treatments, however, are not without risk, making accurate diagnosis of stroke all the more important. Several conditions may mimic stroke in the emergency department, with myasthenia being an uncommon stroke mimic. We present two cases of myasthenia presenting as posterior circulation stroke. In one case, the tempo suggested basilar thrombosis. Treatment decisions regarding thrombolysis for stroke must be made rapidly. Stroke mimics continue to present a diagnostic challenge, myasthenia included. Accurate diagnosis is essential to avoid unnecessary hazard, as well as to implement effective treatment for the appropriate diagnosis.