Large-scale pruning, the removal of long neuronal processes, is deployed widely within the developing nervous system and is essential for proper circuit formation. InDrosophilathe dendrites of the class IV dendritic arborization sensory neuron ddaC undergo large-scale pruning by local degeneration controlled by the steroid hormone ecdysone. The molecular mechanisms that control such events are largely unknown.To identify new molecules that orchestrate this developmental degeneration, we performed a genetic interaction screen. Our approach combines the strength ofDrosophilaforward genetics with detailedin vivoimaging of ddaC neurons. This screen allowed us to identifyheadcase(hdc) as a new gene involved in dendrite pruning.hdcis evolutionarily conserved, but the protein's function is unknown. Here we show thathdcis expressed just before metamorphosis in sensory neurons that undergo remodeling.hdcis required in a cell-autonomous manner to control dendrite severing, the first phase of pruning. Our epistasis experiments with known regulators of dendrite pruning revealhdcas a founding member of a new pathway downstream of ecdysone signaling.