PURPOSE: To evaluate the association between birth characteristics, including parental sociodemographic characteristics, and early-onset pituitary adenoma (PA) and craniopharyngioma. METHODS: Leveraging the population-based California Linkage Study of Early-onset Cancers, we identified the birth characteristics of incident cases with PA (n = 1,749) or craniopharyngioma (n = 227) who were born from 1978 to 2015 and diagnosed 1988-2015, as well as controls in a 50:1 ratio matched on birth year. Adjusted odds ratios (OR) and 95% confidence interval (CI) estimates were computed using unconditional multivariable logistic regression. RESULTS: Males had a lower risk of PA than females (OR = 0.37, 95%CI: 0.34-0.41), and Black (OR = 1.55, 95%CI: 1.30-1.84) or Hispanic (OR = 1.53, 95%CI: 1.34-1.74) individuals had a higher risk compared to non-Hispanic Whites. Older maternal age was positively associated with PA (OR = 1.09, 95%CI: 1.04-1.15 per 5 years, p < 0.01), as was higher maternal education (OR = 1.12, 95%CI: 1.04-1.20 per year, p < 0.01). There were no statistically significant associations between birthweight (OR = 1.04, 95%CI: 0.99-1.09 per 500 g, p = 0.12), birth plurality, or birth order and PA. When stratified by race and ethnicity, the significant association with maternal education was identified only for non-Hispanic White individuals. On multivariable logistic regression, no statistically significant associations were identified between birth characteristics and incidence of craniopharyngioma, except that risk was higher among Hispanic (OR = 1.45, 95%CI: 1.01-2.08) compared to non-Hispanic White individuals. CONCLUSION: In this large, population-based study, female sex, older maternal age, higher maternal education, and Hispanic ethnicity and Black race compared to non-Hispanic White race, were associated with an increased risk of PA in children and young adults.