A 41 year-old female presented with swelling of lower extremities and polyarthralgia involving both knee joints. Physical examination revealed presence of finger clubbing, tenderness and pain-on-motion in knee and foot joints. A chest X-ray film showed a solitary tumor in the right mid-lung field. There were subperiosteal new bone formation and radioisotope accumulation in the legs bilaterally. The clubbing, periostitis and arthritis confirmed a diagnosis of hypertrophic osteoarthropathy. Adenocarcinoma was the biopsy diagnosis of the lung tumor. The characteristic features of hypertrophic osteoarthropathy resolved after surgical resection of the pulmonary lesion followed by chemotherapy. This case demonstrates a typical example of identification of a treatable malignant condition by rheumatic symptoms.