Left atrial enlargement (LAE) has adverse prognostic implications in hypertension. We sought to determine the accuracy of five electrocardiogram (ECG) criteria for LAE in hypertension relative to cardiac magnetic resonance (CMR) gold standard and investigate the effect of concomitant obesity. One hundred and thirty consecutive patients (age: 51.4 ± 15.1 years, 47% male, 51% obese, systolic blood pressure (BP): 171 ± 29 mm Hg, diastolic BP: 97 ± 15 mm Hg) referred for CMR (1.5 T) from a tertiary hypertension clinic were included. Patients with concomitant cardiac pathology were excluded. ECGs were assessed blindly for the following: (1) P-wave > 110 ms, (2) P-mitrale, (3) P-wave axis < 30°, (4) area of negative P-terminal force in V1 > 40 ms.mm and (5) positive P-terminal force in augmented vector left (aVL) > 0.5 mm. Left atrial volume ≥ 55 ml m-2, measured blindly by CMR, was defined as LAE. Sensitivity, specificity, positive predictive value, negative predictive value, accuracy and area under the receiver operator curve were calculated. The prevalence of LAE by CMR was 26%. All the individual ECG LAE criteria were more specific than sensitive, with specificities ranging from 70% (P-axis < 30°) to 99% (P-mitrale). Obesity attenuated the specificity of most of the individual ECG LAE criteria. Obesity correlated with significant lower specificity (48% vs 65%, P < 0.05) and a trend towards lower sensitivity (59 vs 43%, P = 0.119) when ≥ 1 ECG LAE criteria were present. Individual ECG criteria of LAE in hypertension are specific, but not sensitive, at identifying LAE. The ECG should not be used to excluded LAE in hypertension, particularly in obese subjects.