Background: Pediatric brain tumor survivors are at risk for poor social outcomes. It remains unknown whether cognitive sparing with proton radiotherapy (PRT) supports better social outcomes relative to photon radiotherapy (XRT). We hypothesized that survivors treated with PRT would outperform those treated with XRT on measures of cognitive and social outcomes. Further, we hypothesized that cognitive performance would predict survivor social outcomes. Procedure: Survivors who underwent PRT (n=38) or XRT (n=20) participated in a neurocognitive evaluation >1 year post-radiotherapy. Group differences in cognitive and social functioning were assessed using ANCOVA. Regression analyses examined predictors of peer relations and social skills. Results: Age at evaluation, radiation dose, tumor diameter, and sex did not differ between groups (all p>0.05). However, XRT participants were younger at diagnosis (XRT M=5.0 years, PRT M=7.6 years) and further out from radiotherapy (XRT M=8.7 years, PRT M=4.6 years). The XRT group performed worse than the PRT group on measures of processing speed (p=0.01) and verbal memory (p<0.01); however, social outcomes did not differ by radiation type. The proportion of survivors with impairment in peer relations and social skills exceeded expectation (2(1)=38.67, p<0.001; 2(1)=5.63, p<0.05), and verbal memory approached significance as a unique predictor of peer relations (t=-2.01, p=0.05). Total tumor RT dose significantly predicted social skills (t=-2.23, p<0.05). Conclusions: Regardless of radiation modality, survivors are at risk for social challenges, with one-quarter being socially excluded or undervalued. Deficits in verbal memory may place survivors at particular risk. Results support monitoring of cognitive and social functioning throughout survivorship.