Mutations of the syntaxin binding protein 1 (STXBP1) have been associated with severe infantile epileptic encephalopathies (Ohtahara syndrome and West syndrome), but also with moderate to severe cognitive impairment and nonsyndromic epilepsy. We have studied a white infant who presented with focal seizures at age 2 weeks. Brain imaging was unremarkable. The electroencephalograph (EEG) demonstrated normal background frequency content but with multifocal sharp waves and no evidence of the typical patterns associated with Ohtahara or West syndrome. Therapy with levetiracetam and oxcarbazepine effectively managed the seizure episodes. Investigation of genes associated with infantile forms of epilepsy such as SCN1A, SCN1B, and ARX were negative, but we identified a novel single-nucleotide duplication mutation, c.931dupT (p.S311FfsX3), in exon 11 of the STXBP1 gene. This previously unreported STXBP1 mutation in a subject with neonatal-onset focal seizures broadens the spectrum of clinically relevant human disorders caused by STXBP1 mutations.