Objective: To provide age- and sex-specific estimates of methylphenidate use and to determine use changes over a 2-year period. Study design: We examined the first and second data collection cycles of the National Longitudinal Survey of Children and Youth, a Canadian household survey of children. Participants were children aged 2 years to 11 years at both the first and second cycles whose mothers responded; thus, 16,798 (13,059) children were assessed for the first (second) cycle. Logit modeling was used to estimate prevalence of methylphenidate use, to determine sex and age effects on prevalence, and to examine use changes from cycle 1 to 2. Results: Methylphenidate prevalence ranged from 0.09% to 3.89% across 2- to 11-year old children from the first cycle. Boys were 4.6 times more likely than girls to consume methylphenidate. Use was >4 times greater among 6- to 7-year-old children compared with 4- to 5-year-old children and almost 2 times greater among 8- to 9-year-old children compared with 6- to 7-year-old children. Methylphenidate prevalence increased by 36% from cycle 1 to 2. Conclusions: Methylphenidate prevalence was relatively low. Boys and school-age children had higher rates of methylphenidate use, and use among 2- to 11-year-old children appeared to be increasing over time. (J Pediatr 2002;141:71-5)