The aim of the present paper was to evaluate the influence of a family history of hypertension and the degree of obesity as indicated by tertiles of body mass index on ambulatory blood pressure (BP) values in large number (n = 406) of young mild essential hypertensives. Positive family history of hypertension was associated with a significant increase in 24h ambulatory systolic blood pressure (SBP). The difference was most pronounced in the upper tertile of body mass index with almost 6 mm Hg difference between patients with and without a family history of hypertension. Both the degree of obesity and family history of hypertension had significant effects on 24h diastolic blood pressure (DBP). Twenty four hour DBP was highest in the upper tertile of body mass index in the hypertensives with a positive family history, representing an increase of 5 mm Hg compared with patients with a negative family history in the lower tertile. We conclude that mild hypertensives with a positive family history of hypertension are characterised by higher ambulatory BP than patients without parental hypertension and similar supine BP. Furthermore, our results indicate that in mild hypertensives the increase in DBP with body mass index is underestimated by conventional sphygmomanometry.