The diagnosis of hypertrophic cardiomyopathy (HCM) can often be difficult. Traditionally, it has been a diagnosis of exclusion, requiring the demonstration of left ventricular hypertrophy (LVH) in the absence of other causes, such as systemic hypertension or aortic stenosis.1 ,2 Early reports focused on the presence of asymmetrical hypertrophy with an outflow tract gradient (hence the acronym HOCM) but it has become clear that this is not the most common appearance.3-7 Furthermore, recent reports of genotypically affected individuals without hypertrophy, who are nevertheless at risk of sudden death,8 further complicate the situation. Recently, McKenna and colleagues9 proposed modified criteria for the diagnosis of HCM, which overcome some of the problems associated with the conventional criteria (table 1). The new proposed criteria highlight the importance of a comprehensive family history and 12 lead electrocardiogram (ECG) over the echocardiogram in the diagnosis of HCM. Even then, extreme care must be taken because systematic family screening programmes have identified patients who are phenotypically normal but have affected siblings and offspring. These carriers can be missed and their progeny miscoded with less rigorous protocols. Diagnosis can only be 100% reliable when all the implicated gene loci have been identified. Until then the combination of ECG and echocardiography, in conjunction with other clinical information, remain the most useful tests for the diagnosis of patients with HCM. Here, we discuss some of the pitfalls encountered in the echocardiographic evaluation of HCM.