We conducted a retrospective cohort study in children <13 yr with traumatic brain injury (TBI) at a Level 1 pediatric trauma center to describe risk factors for intraoperative hypotension (IH) during emergent decompressive craniotomy. Between 1994 and 2004, 108 children underwent emergent decompressive craniotomy for TBI. Overall, 56 (52%) patients had IH. Independent risk factors for IH were each 10 mL estimated blood loss/kg (ARR 1.15 95% CI 1.08-1.22), each mm of computed tomography (CT) midline shift (ARR 1.04 95%CI 1.01-1.07), each 10 mL of CT lesion volume (ARR 1.03 95%CI 1.01-1.05), and emergency department (ED) hypotension (5/5 patients with ED hypotension had IH). CT midline shift > or =4 mm predicted IH (ARR 1.67 95% CI 1.06-2.63), independent of blood loss. IH occurred frequently during emergent decompressive craniotomy in children with TBI. ED hypotension, blood loss, CT lesion volume, and CT midline shift predicted IH. Anesthesiologists can expect children with preoperative CT midline shift > or =4 mm to have IH during this procedure.