The aim of this study was to assess the impact of obesity and low birth weight on both office and ambulatory blood pressure (BP) values, as well as on aortic-derived parameters in youths. A total of 422 white youths, from 10 to 18 years of age, were included. Subjects were divided into 4 groups according to the presence (234; 55%) or the absence (188; 45%) of obesity and according to low (114; 27%) or normal (308; 73%, birth weight. Spacelabs 90207 was used to measure ambulatory BP during a 24-hour period. SphygmoCor radial/aortic transform software was used to estimate aortic pressure waveform. Office, 24-hour, daytime, and nighttime systolic BP values were significantly higher in those subjects with low birth weight who became obese. The lowest BP values were present in nonobese subjects in the absence of low birth weight. In the middle, with similar BP values, were nonobese subjects with low birth weight and obese subjects in the absence of low birth weight. No interaction existed between obesity and low birth weight in the office (P=0.165) or ambulatory (P=0.603) systolic BP values. Augmentation index, an estimate of the pulse wave reflection, was significantly higher in the nonobese low birth weight group when compared with the other groups after controlling for height, heart rate, and diastolic BP. A significant interaction between low birth weight and obesity (P<0.005) existed. In conclusion, although the low birth weight children who become obese have the highest systolic BP values, the presence of obesity blunts the increment of the reflecting wave observed in low birth weight subjects.