The fne (found-in-neurons) locus encodes one of the three paralogs of the ELAV gene family of Drosophila melanogaster. Members of this family are found throughout metazoans and encode RNA-binding proteins with primarily neuronal localization, but with remarkably diverse functions given their high level of amino acid sequence conservation. The first identified member of the family, elav of Drosophila is a vital gene. Mutations in the second Drosophila elav paralog, rbp9, are viable but female sterile. No alleles of fne were previously available. FNE protein is normally present in the cytoplasm of all neurons throughout development. Here we describe the generation and characterization of fnenull mutations by homologous recombination. In contrast to elav and similar to rbp9, fnenull mutants are viable, but exhibit a specific and fully penetrant fusion of the β-lobes in their mushroom bodies (MB), a paired neuropil of the central brain involved in a variety of complex behaviors. Mutant males have reduced courtship indices, but normal short- and long-term courtship memory. Our data show that fne has specific functions which are non-overlapping with the other two family members, namely in courtship behavior and in the development of the adult MB. The data further show that courtship memory does not require intact β-lobes in the MB.