Background Although metabolic syndrome (MetS) is an important clinical condition, evidence is scarce on how often doctors successfully diagnose this syndrome. Aims To assess the extent of doctors' diagnosis of MetS and its components in cardiology outpatient setting and whether such diagnosis affects the way patients are counselled on lifestyle modification. Methods This is a multicentre cross-sectional study on randomly selected clinical notes at ambulatory cardiology clinics in three academic centres in the USA. We abstracted data on cardiovascular risk factors, and examined whether doctors documented a diagnosis of MetS and its components. Results Of 511 participants who satisfied our inclusion criteria, the MetS was present in 246 participants (48%). The proportions with which a doctor correctly documented diagnoses were: MetS 9.3% (23/246), obesity 60% (119/197), elevated blood pressure 74% (305/412), elevated fasting glucose 17% (49/291), reduced high density lipoprotein cholesterol 10% (18/190) and elevated triglycerides 20% (32/164). This pattern of diagnoses, less frequent with dyslipidaemia and elevated fasting glucose compared with the rest, was persistently observed regardless of sex, age, and presence or absence of MetS. Those diagnosed were more likely to receive a recommendation of weight loss or increase in physical activity than those undiagnosed: 91% (21/23) versus 37% (82/223) for weight loss, and 83% (19/23) versus 26% (58/223) for increase in physical activity (P < 0.001 for both). Conclusions Our data indicate that MetS and its components are commonly underdiagnosed in cardiology outpatient setting. Better diagnosis may lead to better counselling on lifestyle changes and improvement in the quality of care. © 2010 Blackwell Publishing Ltd.