This study aimed to identify the determinants of intellectual and developmental outcomes following pediatric hemispherotomy in a large, contemporary multicenter cohort. We retrospectively analyzed the intellectual and developmental outcomes of 296 children and adolescents who underwent hemispherotomy between 2000 and 2016 and received a standardized postsurgical evaluation of intelligence or developmental quotient (IQ/DQ). Outcomes at the last follow-up were classified into four categories: normal (IQ/DQ > 85), mildly impaired (IQ/DQ = 70-84), moderately impaired (IQ/DQ = 55-69), or severely impaired (IQ/DQ < 55). Determinants of these outcomes were identified using ordinal regression modeling with imputation for missing data. At a median follow-up of 2.1 years (interquartile range = 1.3-5.3), 84% of the children and adolescents were seizure-free, and 60% had discontinued antiseizure medication (ASM). Intellectual and developmental functioning at the last assessment was normal in 11% of the patients, mildly impaired in 16%, moderately impaired in 22%, and severely impaired in 51%. Higher functioning was less likely in patients with polymicrogyria as the underlying etiology (odds ratio [OR] = .3 [.11-.77], p = .013), those with contralateral magnetic resonance imaging abnormalities (OR = .47 [.22-.99], p = .047), and those who continued ASM after surgery (OR = .51 [.29-.9], p = .021). Conversely, patients with a later age at epilepsy onset were more likely to achieve higher functioning (OR = 1.16 [1.04-1.3], p = .011). Age at epilepsy onset, underlying etiology, presence of bilateral structural brain abnormalities, and postsurgical ASM management were key determinants of intellectual and developmental outcomes following hemispherotomy. These findings underscore the importance of timely ASM discontinuation as the only modifiable factor that may optimize intellectual and developmental trajectories. Although direct presurgical comparisons were not possible, the observed associations provide valuable insights into factors influencing cognitive outcomes.