Milk formula feeding can elevate insulin-like growth factor-1 levels, possibly impacting leukemogenesis. The intent of the current study is to examine the associations between infant feeding practices and age at introduction of solids on risk of childhood acute lymphoblastic leukemia (ALL). Incident cases of infant and childhood (aged ≤14 years) ALL (n = 142) were enrolled in a case-control study. Cases were frequency matched on age, sex, race, and ethnicity to two sets of controls (n = 284 total). Multivariable logistic regression was used to determine the association between infant feeding practices and age at the introduction of solids and the odds ratio of ALL. In adjusted multivariable analyses, each additional month of formula feeding was associated with a 1.17 (1.09-1.25) odds ratio; each additional month of age at introduction of solids was associated with a 1.18 (1.07-1.30) odds ratio. In this study, longer duration of formula feeding and later age at the introduction of solid foods were independently associated with increased risk of ALL. Additional studies are needed to address the factors influencing duration of formula feeding and delayed introduction of solids. The results support the potential role of energy balance in early life as a contributor to risk for pediatric acute lymphoblastic leukemia.