The classification of subjects as nocturnal hypertensives in accordance with non-dipping (i.e. systolic blood pressure - BP - fall <10%) is less reproducible as compared to the fixed cut-off limits method (nocturnal BP means >120/70 mm Hg). The present study was carried out to assess if nocturnal hypertension defined by fixed cut-off limits may be a better predictor of left ventricular hypertrophy (LVH) than to non-dipping. Echocardiography and 24-h ambulatory blood pressure monitoring were performed in 223 subjects. Logistic regression showed that nocturnal hypertension defined by fixed cut-off limits was a significant predictor of LVH (OR=11.1, 95%CI=3.0-40.1) whereas non-dipping was not (OR=1.4, 95%CI=0.4-5.5). No interaction was detected (p<.3). These results suggest that the definition of nocturnal hypertension based on fixed cut-off values is a better predictor of left ventricular hypertrophy than non-dipping.