Abstract Body: Introduction: surgical evacuation of non-acute subdural hematoma (SDH) for rapid brain decompression and middle meningeal artery embolization (MMAe) to prevent re-bleeding as a surgical adjunct is becoming a dominant treatment paradigm of symptomatic SDH. However, this approach requires two different interventions with their associated risks, prolonged ICU/hospital stay and increased costs. An endovascular technology was developed for transvascular access to the intradural space, drainage of SDH and MMAe. We report the procedural results and 6-month follow up of the first three consecutive patients treated with this technology. Methods: a prospective, single-arm, first-in-human study (EMBODRAIN Study) was conducted to evaluate the safety and feasibility of endovascular drainage of non-acute SDH and MMAe using a purpose-built endovascular technology (Endovascular Horizons, Inc). Results: three consecutive patients (males, 76 years ±5) were treated and completed the pre-specified 6 months follow-up. Acute clinical success (defined as MMAe and transvascular drainage of the SDH with no conversion to open surgical drainage) and acute technical success (defined as ability to create a leak-proof transvascular passageway and access the intradural space, drain the SDH and occlude the MMA) was achieved in all cases (3/3). No Serious Adverse Events (SAE) were recorded at 30-days. The SDH volume at baseline (before intervention) was on average 296 ml, and decreased immediately post-procedurally to 25ml, corresponding to a 92% volumetric reduction on average. The SDH thickness at baseline was on average 25 mm, and decreased post-procedurally to 11 mm. The midline shift at baseline was on average 8 mm, and decreased post-procedurally to 3 mm. At 6-months the head CTs showed an average SDH volume of 8ml, SDH thickness of 3mm, and midline shift of 0mm. The pre-morbid Modified Rankin Scale Score was 0.33 on average, was 3.66 at presentation with the SDH, and decreased to an average of 2.33 at 72hrs post-intervention. At 6 weeks, 3 months and 6 months follow-up, all patients were found to have a mRS of 0. During the study duration there were no SDH recurrence or progression requiring surgery, hospital readmission and deterioration in neurological function. Conclusions: this report presents the first cohort of patients with symptomatic non-acute subdural hematomas to successfully undergo endovascular drainage of SDH and MMAe in a single, fully endovascular procedure.