RATIONALE: Familial hypercholesterolemia (FH) predisposes patients to premature cardiovascular disease, with the process of atherosclerosis initiated in early childhood. OBJECTIVE: As part of an ongoing trial to assess the efficacy and safety of rosuvastatin in children with FH aged 6 to 17 years, we report the differences in carotid intima-media thickness (cIMT) at baseline between children with FH and their unaffected siblings. METHODS AND RESULTS: B-mode ultrasound measurements of the carotid artery were made in 196 children with FH and 64 of their siblings. Mean (±SE) cIMT in children with FH was significantly greater than that of unaffected siblings (0.398±0.052 versus 0.377±0.045 mm; P<0.001). A significantly greater cIMT value was observed before the age of 8 years. Multivariable analyses showed that age, male sex, and presence of FH were independent predictors of cIMT. CONCLUSIONS: The difference in mean cIMT between children with FH and their unaffected siblings may be significant as early as age 8 years. This study confirms the need for early cholesterol lowering in this high-risk population. These patients participating in a carefully monitored study will help assess the long-term efficacy on cIMT and safety of statin therapy in young children.