Objectives: To determine the immediate post-operative course and outcome of pediatric patients with complicated acute mastoiditis (CAM) following surgical treatment. Study Design: A retrospective chart review of children diagnosed with CAM who underwent mastoid surgery during 2012-2019. Setting: Tertiary care university hospital. Participants: the study includes 33 patients, divided into two groups: 17 patients with subperiosteal abscess (SPA) alone - single complication group (SCG) and 16 patients with SPA and additional intracranial or intratemporal complications -multiple complications group (MCG). Main Outcome Measures: post-operative fever course and pattern (POF). Results :33 patients belong to the SCG 17(51%) and 16(49%) belonged to the MCG, respectively. 6/17(35.3%) SCG patients experienced POF vs. 12/16(75%) in the MCG (P=0.012). At post-operative day 2 (POD2), 10/13(77%) febrile patients belonged to MCG and 3/13(23%) to SCG (P=0.013). POF was recorded until POD6 in both groups. Seven patients, all from MCG with POF, underwent second imaging with no new findings. Conclusion: Following a cortical mastoidectomy for CAM, POF is not unusual in the first 6 days and seem to be benign condition. POF is more common, higher, and persistent for a longer duration in MCG compared with SCG. At POD 6, fever is expected to normalize in both groups, so if fever persists further evaluation should be considered.