['We compared the frequency of a binary endocardial appearance in patients with hypertrophic cardiomyopathy (HCM) and Anderson-Fabry disease (AFD).', 'A recent study suggested that a binary endocardial appearance is a highly sensitive and specific discriminator of AFD from other causes of hypertrophic cardiomyopathy (HCM).', 'Fourteen patients with AFD (55.4 +/- 9.9 years, 9 men) and 14 patients with HCM (57.2 +/- 10.9 years, 9 men) were randomly selected from a dedicated patient database. Two-dimensional echo images were blindly reviewed by 2 experienced echocardiographers.', 'Maximum left ventricular (LV) wall thickness, LV end-systolic dimension, fractional shortening, and left atrial size were similar in the 2 patient groups. The LV end-diastolic dimension was smaller in patients with HCM (p = 0.04). A binary sign was present in 8 of 28 patients (29%). The sensitivity and specificity of the binary sign as a discriminator of AFD from HCM were 35% and 79%, respectively. A binary sign was present in only 1 patient with LV wall thickness <15 mm.'] Is the binary endocardial appearance a poor discriminator of Anderson-Fabry disease from familial hypertrophic cardiomyopathy?