Potassium channel subunits encoded by several genes of the KCNQ family underlie the M-current. Specifically, KCNQ2 and KCNQ3 play a major role at most neuronal sites. Mutations in KCNQ2 or KCNQ3 that reduce the M-current are responsible for benign familial neonatal seizures, a rare autosomal dominant idiopathic epilepsy of the newborn. The aim of this study was to investigate a single family with benign familial neonatal seizures for mutations in KCNQ genes and to analyze the association of mutation type with disease prognosis. A family in which members in several generations had signs and symptoms compatible with a diagnosis of benign familial neonatal seizures had DNA testing with single-stranded conformation polymorphism analysis for various mutations known to cause benign familial neonatal seizures. A novel KCNQ2 mutation c.63-66delGGTG (p.K21fsX40), causing a framework shift and early chain termination, was identified in the affected family members. In all cases, there was complete remission of the seizures after the neonatal period. This KCNQ2 mutation has implications for diagnosis and prognosis of familial neonatal seizures. Its presence suggests a benign disease with good prognosis and its identification can spare patients and physicians the need for extensive investigations or prolonged therapy.