Respiratory syncytial virus F-protein (RSV-F) is poorly expressed from DNA expression plasmids containing the wild type RSV-F open reading frame. By codon optimization, premature polyadenylation signals were deleted and a striking enhancement of RSV-F expression levels was achieved. Therefore, the immunogenicity and efficacy of wild type DNA vaccines were compared to codon optimized expression plasmids encoding full-length RSV-F or its ectodomain. Mice were immunized twice with the different DNA vaccines followed by an RSV challenge. Only codon optimized DNA vaccines and in particular the one encoding the ectodomain of RSV-F induced substantial antibody levels and reduced viral load 13-170-fold. Thus, codon optimization enhances the immunogenicity and efficacy of RSV encoding DNA vaccines.