The development of the hypertrophic cardiomyopathy (HC) phenotype with left ventricular (LV) hypertrophy usually occurs in adolescence, and documentation of patients with later onset of wall thickening during adulthood is rare. We report 4 patients with asymptomatic, nonobstructive HC (3 women and 1 man) who were studied with serial cardiovascular magnetic resonance imaging or echocardiography. In these patients, LV wall thickening, confined to the apex and the contiguous distal portions of the ventricular septum and free wall, appeared in midlife and beyond. These patients were >40, >50, or >70 years old when the hypertrophy became evident. The maximum LV wall thickness was 14 to 25 mm (mean 18), with a “spade” deformity of the distal chamber, associated with a nondilated cavity and normal ejection fraction (65% to 80%), in the absence of mitral valve systolic anterior motion. In each patient, similar electrocardiographic patterns with similar diffuse and marked T-wave inversion (with or without increased precordial voltages) preceded the appearance of the HC phenotype on the imaging studies. In conclusion, the recognition that the onset of LV hypertrophy in HC can be delayed well into adulthood (and even to advanced age) has important implications regarding the clinical screening practices for families, and suggests the potential value of extending prospective serial imaging beyond adolescence in some relatives. Electrocardiographic repolarization abnormalities can predict the future development of apical LV hypertrophy in adults with HC.