Acquired clubbing of the digits and hypertrophic osteoarthropathy are closely related disorders of unknown etiology that derive special significance from their frequent association with serious underlying diseases of the thorax or abdomen. Most importantly, clubbing or HOA may provide the first clinical indication of a chronic infection or an intrathoracic neoplasm. However, clubbing is easily overlooked on physical examination, and hypertrophic osteoarthropathy is often mistaken for some other disorder. The diagnosis of clubbing is based on the finding of an increase in the soft tissue at the base of the finger or toenails. Of the several objective criteria that have been proposed for the diagnosis of digital clubbing, the best documented and most practical is an increase in the ratio of the distal phalangeal depth (DPD) to the interphalangeal depth (IDP) of the index finger to 1.0 or greater. Hypertrophic osteoarthropathy is characterized in advance cases by the combination of digital clubbing, periostitis of the long bones, arthritis-like changes in the knees, elbows, ankles, and wrists, and swelling of the soft tissues in the distal extremities. Bone scintigraphy has emerged as the most sensitive test for HOA; in fact, a bone scan may show evidence of periostitis in patients with no other signs, symptoms, or radiographic abnormalities of the disorder. The symptoms of HOA respond to anti-inflammatory agents, and to ablation or cure of the underlying disorder.