Maintenance of proper neuronal excitability is vital to nervous system function and normal behavior. A subset of Drosophila mutants that exhibit altered behavior also exhibit defective motor neuron excitability, which can be monitored with electrophysiological methods. One such mutant is the P-element insertion mutant bemused (bem). The bem mutant exhibits female sterility, sluggishness, and increased motor neuron excitability. The bem P element is located in the large intron of the previously characterized translational repressor gene pumilio (pum). Here, by several criteria, we show that bem is a new allele of pum. First, ovary-specific expression of pum partially rescues bem female sterility. Second, pum null mutations fail to complement bem female sterility, behavioral defects, and neuronal hyperexcitability. Third, heads from bem mutant flies exhibit greatly reduced levels of Pum protein and the absence of two pum transcripts. Fourth, two previously identified pum mutants exhibit neuronal hyperexcitability. Fifth, overexpression of pum in the nervous system reduces neuronal excitability, which is the opposite phenotype to pum loss of function. Collectively, these findings describe a new role of pum in the regulation of neuronal excitability and may afford the opportunity to study the role of translational regulation in the maintenance of proper neuronal excitability.