Blood pressure was measured in 864 young people aged 16-24 years, 8 years after both of their parents had their blood pressures measured as part of the screening phase of the Medical Research Council Mild Hypertension Trial. Only 29% of offspring with a conventional 'family history of hypertension', defined in terms of having at least one parent with a score in the top 10% of the distribution, had a blood pressure score in the top 20% after 8 years. The positive predictive value was increased to 38% in offspring with two parents in the top 20%, but only 4% of offspring met this definition and only 7% of offspring in the top 20% after 8 years were identified by this method. Sensitivity was increased to 46% in offspring with at least one parent in the top 20%, but 33% of offspring met this definition and 74% of them did not have a blood pressure level in the top 20% after 8 years. It is concluded that parental blood pressure data are of limited value for the prediction of high blood pressure in young people and provide no scientific basis for a high risk strategy of prevention.