Benign familial neonatal convulsions (BFNC) is a rare autosomal dominant seizure disorder usually described to be characterized by a benign course, spontaneous remission and normal psychomotor development. The latter statement had come under consideration when a few case reports of families with less than favorable outcomes were published.Since 1998 a total of 112 families suspected to have BFNC have been referred to our lab for genetic testing. Within this sample we identified private KCNQ2 mutations in 17 BFNC families. For 10 of those 17 families follow up information about the psychomotor development and the outcome were available.In 4 (40%) of the 10 families at least 1 affected individual showed delayed psychomotor development or mental retardation. Three of the four mutations were familial, while the fourth mutation was de novo. Mutations associated with an unfavorable outcome tended to be located within the functionally critical S5/S6 regions of the KCNQ2 gene.Our data raise the question if BFNC can indeed be described as a benign disorder, and which are the genetic and/or environmental factors that influence the outcome.