Hypertrophic obstructive cardiomyopathy (HOCM) has four major features: (1) severe left ventricular hypertrophy, often most prominent in the basal interventricular septum; (2) frequent familial occurrence with autosomal dominant transmission; (3) occurrence of sudden cardiac death that is usually considered to be due to ventricular fibrillation; and (4) presence of hemodynamic evidence of labile intraventricular obstruction. The key papers describing the recognition of each of these features, as well as of various combinations of them, are reviewed in this paper. Particular attention is focused on the very frequent finding of marked lability of intraventricular obstruction. The recognition of this fourth and last major feature in 1959 makes 2009 the golden anniversary year marking completion of the description of the major features of HOCM.