Animals can respond differently to a sensory cue when in different states. Here, we show that certain odors repel well-fed Drosophila larvae but attract food-deprived larvae and how feeding state flexibly alters neural processing in an early olfactory circuit, the antennal lobe, to determine the behavioral valence of a sensory cue. Odor valence is assigned by a neuronal architecture that controls a switch between two separate projection neuron output pathways that mediate opposite behavioral responses. A uniglomerular projection neuron pathway mediates odor attraction whereas a multiglomerular projection neuron pathway mediates odor repulsion. The serotonergic CSD neuron in the antennal lobe is a critical regulator of this neuronal and behavioral switch. CSD selects an appropriate behavior by shifting patterns of serotonergic modulation and glutamatergic inhibition onto each output pathway. The antennal lobe is a decision-making circuit for innate behavioral responses that uses feeding state to determine an odor’s valence.