We have reported the presence of OHC apoptosis and necrosis in the organ of Corti following exposure to intense noise. The current study was designed to investigate the rapidity and the initial pattern of outer hair cell (OHC) death induced by exposure to impulse noise. Chinchillas were exposed to 75 pairs of impulse noise at 155dB peak sound pressure level presented over a time period of 75s. At 5 or 30min after the noise exposure, the cochleae were examined for morphological and biological indicators of apoptosis and necrosis. In the cochleae collected within 5min after the 75-s noise exposure, there were clear signs of nuclear condensation and cell body shrinkage, suggesting the presence of OHC apoptosis. Apoptotic OHCs were further detected by positive staining of TUNEL and caspase-3 assays. In contrast to the rapid development of nuclear condensation, appearance of nuclear swelling, a necrotic phenotype, appeared at 30min after the noise exposure. The results of the study demonstrate that induction of OHC apoptosis after the noise exposure is an extremely rapid process.