AbstractIschemic stroke of the paramedian thalamus is a rare differential diagnosis in sudden altered vigilance states. While efforts to describe clinical symptomatology exist, data on the frequency of paramedian thalamic stroke as a cause of sudden impaired vigilance and on accompanying clinical signs and outcome are scarce. We retrospectively analyzed consecutive patients admitted to a tertiary stroke center between 2010 and 2019 diagnosed with paramedian thalamic stroke. We evaluated frequency of vigilance impairment (VI) due to paramedian thalamic stroke, accompanying clinical signs and short-term outcome in uni- versus bilateral paramedian lesion location. Of 3896 ischemic stroke patients, 53 showed a paramedian thalamic stroke location (1.4%). VI was seen in 29/53 patients with paramedian thalamic stroke and in 414/3896 with any stroke (10.6%). Paramedian thalamic stroke was identified as causal to VI in 3.4% of all patients with initial VI in the emergency department and in 0.7% of all ischemic stroke patients treated in our center. Accompanying clinical signs were detected in 21 of these 29 patients (72.4%) and facilitated a timely diagnosis. VI was significantly more common after bilateral than unilateral lesions (92.0% vs. 21.4%; p < 0.001). Patients with bilateral paramedian lesions were more severely affected, had longer hospital stays and more frequently required in-patient rehabilitation. Paramedian thalamic lesions account for about 1 in 15 stroke patients presenting with impaired vigilance. Bilateral paramedian lesion location is associated with worse stroke severity and short-term outcome. Paying attention to accompanying clinical signs is of importance as they may facilitate a timely diagnosis.