Blood pressure values are known to vary with age and body size. The effect of sexual maturity was explored in 746 patients in an adolescent clinic. Systolic blood pressure for boys and girls showed an increase with a change from Tanner stage 2 to 3. Diastolic blood pressure did not increase. Both systolic and diastolic blood pressures showed a weight effect that was generally maintained within the Tanner stages. The gradual increase in blood pressure for large groups of adolescents would appear to be the result of the aggregate increase in size (weight) resulting from the asynchronous growth spurts of individuals studied. Consequently, those individuals with a strikingly early or late onset of maturation may have erroneous interpretations of their blood pressure. As biologic outliers, the borderline hypertensive who matures early may be overidentified, while the late maturer might go unrecognized.