Acetylcholine is the major excitatory neurotransmitter in the central nervous system of insects. Mutant analysis of the Dalpha7 nicotinic acetylcholine receptor (nAChR) of Drosophila shows that it is required for the giant fiber-mediated escape behavior. The Dalpha7 protein is enriched in the dendrites of the giant fiber, and electrophysiological analysis of the giant fiber circuit showed that sensory input to the giant fiber is disrupted, as is transmission at an identified cholinergic synapse between the peripherally synapsing interneuron and the dorsal lateral muscle motor neuron. Moreover, we found that gfA1, a mutation identified in a screen for giant fiber defects more than twenty years ago, is an allele of Dalpha7. Therefore, a combination of behavioral, electrophysiological, anatomical, and genetic data indicate an essential role for the Dalpha7 nAChR in giant fiber-mediated escape in Drosophila.