Introduction: We describe the clinical presentation of new-onset refractory status epilepticus of unknown etiology in children. Methods: We analyzed patients within the pediatric Status Epilepticus Research Group (pSERG) cohort with the following inclusion criteria: 1) age 1–21 years; 2) first episode of RSE requiring more than 2 anti-seizure medications (ASM); 3) RSE episode between 06/2011 and 10/2016. We excluded patients with a history of developmental delay and/or epilepsy. We compare these patients to those with a first refractory status epilepticus (RSE) due to an identified etiology. Results: Fifty four patients were eligible. The median age was 5 years (IQR 1.9, 10.6). The most frequent etiologies were infection (15%), febrile status epilepticus (15%) and acute brain lesions (13%). No etiology was found in 18 patients (33%). In the group with unknown etiology, 15 patients (83%) required intubation and the median duration of ICU stay was 4.8 days (IQR 2, 49). These patients received a median of 3 ASM (IQR 2, 4) and 1 continuous infusion (IQR 0, 3). Compared to patients with an etiology, patients with unknown etiology received a larger number of immunotherapies (8 vs 5 patients; p = 0.02), were more often treated with the ketogenic diet (7 vs 2; p = 0.004) and were more likely to have a family history of epilepsy (6 vs 3; p = 0.045). The mean duration of RSE in the group with unknown etiology (12.25 h) was longer than in the group with etiology (4.25 h; p = 0.4). Fifty five percent of the patients with unknown etiology failed to return to baseline function at discharge compared to 36% in patients with an etiology (p = ns). Conclusions: One third of children with a first episode of RSE had an unknown etiology and seemed more likely to have a family history of epilepsy. These patients were more likely to receive immunotherapies and ketogenic diet.