Body weight is controlled by the activation of signal transduction pathways in both the brain and peripheral tissues. Interestingly, although many hypothalamic neuropeptides and receptors have been implicated in the regulation of body weight, the transcriptional and posttranscriptional mechanisms through which these genes are expressed in response to changes in energy balance remain unclear. Our laboratory studies a mouse in which targeted deletion of the neuronal basic helix-loop-helix (bHLH) transcription factor, nescient helix-loop-helix 2 protein (Nhlh2), results in adult-onset obesity. The aim of this work was to use the phenotype of the Nhlh2 knockout mouse and the expression pattern of Nhlh2 to identify genes that are regulated by this transcription factor. In this article, we show that Nhlh2 is expressed throughout the adult hypothalamus. Using dual-label in situ hybridization, we demonstrate that, in the arcuate nucleus of the adult hypothalamus (ARC), Nhlh2 expression can be found in rostral proopiomelanocortin (POMC) neurons, whereas in the paraventricular nucleus (PVN), Nhlh2 is expressed in TRH neurons. In addition, we find that hypothalamic POMC-derived alphaMSH in the ARC and TRH in the PVN are regulated posttranscriptionally via Nhlh2-mediated control of prohormone convertase I and II mRNA levels. This is the first report in which regulation of body weight is linked to the action of a neuronal bHLH transcription factor on prohormone convertase mRNA levels. Furthermore, this work supports a direct role for transcriptional control of neuropeptide processing enzymes in the etiology of adult-onset obesity.