In many countries oxcarbazepine (OXC) has been registered for use as first-line and add-on treatment for patients with partial seizures with or without secondarily generalized seizures (PS) and generalized tonic-clonic seizures without partial onset (GTCS). Its use as monotherapy in children and adolescents with newly diagnosed epilepsy was investigated in this double-blind, randomized, parallel-group comparison with phenytoin (PHT). A total of 193 patients aged 5-18 years with either PS or GTCS were enrolled. After a retrospective baseline assessment, patients were randomized to OXC or PHT in a 1:1 ratio. The double-blind treatment phase comprised two periods: an 8-week flexible titration period; followed by 48 weeks maintenance treatment. In the efficacy analyses, there were no statistically significant differences between OXC and PHT. Forty-nine (61%) patients in the OXC group and 46 (60%) in the PHT group were seizure-free during the maintenance period. In total, 24 patients in the OXC group discontinued treatment prematurely (two for tolerability reasons) compared with 34 in the PHT group (14 for tolerability reasons). The number of premature discontinuations due to adverse experiences was statistically significantly lower in the OXC group than in the PHT group. Moreover, the odds of an individual discontinuing prematurely (regardless of reason) were almost twice as high in the PHT group. This trial provides further support for the efficacy and safety of OXC as first-line treatment in children and adolescents with PS and GTCS. In addition, the results show that OXC in these patients has significant advantages over PHT in terms of tolerability and treatment retention.