To evaluate the efficiency of TALEN technology for introducing mutations into the mouse genome we targeted Scn8a, a member of a multigene family with nine closely related paralogs. Our goal was to generate a model of early onset epileptic encephalopathy by introduction of the Scn8a missense mutation p.Asn1768Asp. We used a pair of TALENs that were highly active in transfected cells. The targeting template for homologous recombination contained a 4 kb genomic fragment. Microinjection of TALENs with the targeting construct into the pronucleus of 350 fertilized mouse eggs generated 67 live‐born potential founders, of which 5 were heterozygous for the pathogenic mutation, a yield of 7% correctly targeted mice. Twenty‐four mice carried one or two Scn8a indels, including 12 frameshift mutations and the novel amino acid deletion p.Asn1759del. Nine off‐site mutations in the paralogs sodium channel genes Scn5a and Scn4a were identified. The data demonstrate the feasibility and efficiency of targeting members of multigene families using TALENs. The Scn8a^tm1768DMm mouse model will be useful for investigation of the pathogenesis and therapy of early onset seizure disorders. genesis 52:141–148. © 2013 The Authors genesis Published by Wiley Periodicals, Inc.