Background: Pediatric brain tumor survivors can experience detrimental effects from radiation treatment. Proton radiation therapy (PRT), which enables better targeting of radiation to tumors, may result in fewer sequelae. This follow-up cross-sectional study examined psychosocial and executive functioning in children and young adults treated with PRT. Procedure: Psychosocial and executive functioning was assessed by standardized parent rating scales for 187 patients. The sample was divided by age at baseline (<6 years [35.8%] and ≥6 years [64.2%]) and PRT field (craniospinal irradiation (CSI [36.9%]) and focal [63.1%]). Rates of impairment were calculated. Results: Mean age was 8.49 years at baseline; mean follow-up interval was 3.84 years. All mean scores were within the normal range and within normative expectation. Younger CSI group had significantly more problem behaviors and lower adaptive skills compared to older CSI or focal groups; however, no significant differences were found between younger PRT groups. There were no significant differences in executive functioning between the four age-by-PRT-field groups. Rates of impairment exceeded expected rates in social withdrawal, somatic concerns, activities of daily living, and metacognitive executive functioning. Age group was not significantly related to impairment rates, although the younger group had more problems with withdrawal, anxiety, activities of daily living, and executive functioning with relatively higher anxiety and withdrawal in the younger CSI group. Conclusions: Psychosocial and executive functioning was within the normal range at follow-up. Younger patients, particularly those treated with CSI, appeared more vulnerable. Screening and proactive intervention are needed to support psychosocial well-being and executive functions.