A 43 year old man was admitted because of fatigue and swelling of the knees. Swelling of both knees, acropachy and turtle-back nails were registered during clinical investigation and laboratory tests showed leucocytosis, increased blood-sedimentation rate and alkaline phosphatase. Leucine aminopeptidase was normal. X-ray showed symmetric metaphyseal periosteal reactions on femora and tibiae of both sides compatible with hypertrophic osteoarthropathy. A parahilar round tumor measuring 5 x 7 cm infiltrating the right upper lobe was detected on chest x-ray suggestive of lung cancer. Pierre-Marie-Bamberger syndrome was diagnosed (hypertrophic osteoarthropathy associated with cancer of the lung). Under radiotherapy to the tumor the osteoarthropathy subsided and alkaline phosphatase returned to normal.