Clubbing and hypertrophic pulmonary osteoarthropathy (HPOA) are two components of a clinical syndrome which is more accurately referred to as hypertrophic osteoarthropathy (HOA). HOA occurs as a rare familial primary form and a more common secondary form, which is always due to an underlying disease process. Secondary HOA is now recognized as the correct term for HPOA. The reason for this confusing nomenclature is that HPOA was historically thought only to occur associated with pulmonary disease. However, this is now recognized to be incorrect since numerous diseases affecting other organ systems, such as congenital cyanotic heart disease, are also complicated by clubbing and secondary HOA. Despite the clinical phenomena of HOA being recognized since the time of Hippocrates, the exact pathophysiological events responsible for these changes remain unknown. Various hypotheses including the production of paraneoplastic hormones, intrapulmonary shunting of blood resulting in peripheral platelet degranulation and the associated elaboration of growth factors, and the reappearance of the embryonic claw due to reactivation of dormant genes have been suggested as plausible mechanisms for this condition, but none is universally accepted. Although pulmonary suppuration commonly gives rise to clubbing and secondary HOA, primary lung neoplasia is responsible for the majority of pulmonary cases of this syndrome, meaning that the manifestation of the clinical phenomena of this condition should be investigated with a great deal of suspicion. Although analgesic agents can treat the pain associated with this syndrome, unfortunately, there is no specific treatment for clubbing and secondary HOA other than eradication of the underlying disease process.