Blood pressure was measured in 730 infants and their mothers within 5 days of birth. Paternal blood pressures were obtained where possible, and follow-up measurements were made on participants at 1 week and 1, 6, 12, 18, and 24 months. Infant blood pressures were adjusted for such variables as age, observer, cuff size, and sleep/activity status. Infant blood pressure correlated with maternal blood pressure corrected for age and observer shortly after birth (r = 0.138, p less than 0.001 for systolic pressure; r = 0.169, p less than 0.001 for diastolic pressure). Father-infant correlations were significant only at 1 month after birth (r = 0.179, p = 0.031; r = 0.250, p = 0.002 for systolic and diastolic pressures respectively), and sibling correlations were significant from 6 months after birth (r = 0.173, p = 0.011 for systolic pressure; r = 0.265, p less than 0.001 for diastolic pressure). Blood pressures of infants before 6 months after birth were not consistently predictive of later pressures, but systolic and diastolic blood pressures 6 and 12 months after birth were significantly and positively related to pressures at later ages (for systolic pressures at 6 and 12 months, r = 0.147, p = 0.003; 6 and 18 months, r = 0.218, p less than 0.001; 6 and 24 months, r = 0.212, p less than 0.001). These results indicate that the familial aggregation of blood pressure and blood pressure tracking can be detected early in life.