Food prices are expected to affect dietary intakes, however, previous findings are mixed and few are based on nationally representative data. We examined the associations of price indices of fast foods (FF-PI) and fruits and vegetables (FV-PI) with dietary intakes and BMI among U.S. children and adolescents using data from the Continuing Survey of Food Intakes by Individuals (CSFII; 1994-1998) for 6759 children (2-9 y) and 1679 adolescents (10-18 y). FF-PI and FV-PI were linked to individuals' CSFII dietary data through city-level geocodes. Main outcomes included intakes of selected nutrients and food groups, a fast food consumption index (FF-CI), diet quality using the 2005 Healthy Eating Index (HEI), and BMI. Among children (2-9 y), a higher FF-PI (by $1) was associated with intakes of lower FF-CI (β ± SE: -0.9 ± 0.3 count/d), higher HEI (6.6 ± 2.5), higher intakes of fiber (2.7 ± 0.7 g/d), calcium (225.7 ± 52.3 mg/d), dairy (172.5 ± 36.2 g/d), and fruits and vegetables (113.3 ± 23.4 cup equivalents/d). FV-PI was inversely related to fiber intake (β ± SE: -3.3 ± 1.5 g/d) and positively associated with BMI (4.3 ± 1.2 kg/m(2)). Less consistent findings were ascribed to FV-PI and among adolescents (10-18 y). Significant associations were almost equally balanced between low and high family income groups, with some significant interactions between food prices and family income observed, particularly among children (2-9 y). Our findings suggest that among U.S. children aged 2-9 y, higher FF-PI is associated with better dietary quality, whereas higher FV-PI is linked to higher BMI and lower fiber intake. Associations varied by family income in children for many dietary intake variables.