Paraneoplastic syndromes are generally caused by ectopic hormone production or immune-mediated tissue destruction caused by neural antigen expression of cancer cells. Here, we present a rare case of paraneoplastic syndrome associated with interstitial pneumonia mimicking lung cancer. Laboratory findings of the concerning patient revealed liver enzyme abnormalities, and elevated level of cancer antigen neuron specific enolase. Electrostimulation demonstrated changes typical of the Lambert-Eaton Myasthenic syndrome (LEMS). Additionally, histopathological findings of the liver confirmed intrahepatic cholestasis. The contrast-enhanced spiral computed tomography on admission showed a soft tissue mass near the main pulmonary artery on the right hilus and bilateral pulmonary infiltrates, which are prominent in the right lower lung field. On the basis of the tomography findings, which suggested the risk of lung cancer, we performed an open lung biopsy. However, biopsy showed the lung pathology to be desquamative interstitial pneumonitis. Fortunately enough, one month later, as a result of delivering the appropriate treatment, the symptoms subsided; and the lung function and the chest radiograph findings improved significantly. In addition, the abnormal values for tumor antigens and liver enzymes returned to normal ranges. After 3 years, he was in remission. These findings suggest that paraneoplastic syndromes can also be associated with benign conditions, which require a careful clinical evaluation for the prevention of misdiagnosis. [Turk J Cancer 2008;38(2):78-82]