• A cross-sectional survey of 142 black and 361 white girls was performed to investigate whether differences in the timing of maturation account for blood pressure differences between same-aged subjects. Data were collected on blood pressure, anthropometric parameters, socioeconomic status, and secondary sex characteristics. Analysis of covariance was used to determine whether blood pressure for black and white girls differed significantly after adjusting for the confounding effects of different body size and sexual maturation distributions of the two groups. Advanced sexual maturation of the black girls contributed as much as the larger body sizes of the black girls to the blood pressure differences found between the black and white girls. Assessment of an individual's stage of sexual maturation at blood pressure measurement should be considered as important as the measurement of height and weight.