We report a rare case of nonsteroidal anti-inflammatory drug-induced pneumonitis in a 72-year-old man taking diclofenac for wound pain after pulmonary resection. The pneumonitis and pleural effusion were predominant on the operative side and resolved rapidly after the diclofenac was discontinued. The diagnosis of drug-induced pneumonitis was based on a lymphocyte stimulation test that was positive for diclofenac sodium and negative for other drugs. This case report demonstrated that surgeons should be aware of the possibility of pneumonitis induced by a nonsteroidal anti-inflammatory drug.