Background: Organ toxicity requiring solid organ transplant (SOT) is a rare but serious effect of cancer treatment. Given restricted donor organ supply, teams must assess CAYACS requiring SOT in relation to potential recipients with non-malignant indications; decisions are limited by scant long-term outcome data. We compared long-term outcomes for CAYACS requiring SOT with other SOT recipients. Methods: All Ontario, Canada children < 18 years at cancer diagnosed 1986-2021 at pediatric centres, and AYA aged 15-21 diagnosed at adult centres for acute leukemia, lymphoma, sarcoma, or testicular cancer between 1992-2012 were identified using population-based clinical databases. Patients with SOT prior to their primary cancer diagnosis were excluded. SOT was identified through linkage to healthcare databases; patients were matched 1:2 to non-malignant SOT recipients by sex, SOT year and type, and birth year. Post-SOT outcomes including overall survival (OS) and post SOT cancers were compared between CAYACS and SOT controls. Results: Among 16,533 CAYA with cancer, 85 received SOT: 46 liver, 18 kidney, 11 lung, and 10 heart. Among liver recipients, 33 (71.7%) were for primary cancer treatment (e.g. hepatoblastoma) vs. 13 (28.3%) for organ toxicity. Median age at original cancer diagnosis was 4 years [interquartile range (IQR) 1-13] and at SOT was 13 (IQR 3-20). CAYACS with SOT as treatment for long-term toxicity (liver subset plus all renal, lung, heart, N = 52) had a median time from cancer diagnosis to SOT of 9 years (IQR 4-16) and experienced lower 10-year OS from time of SOT [67.7%, 95^th confidence interval (95CI) 50.8-79.9] vs. SOT matched controls [86.0% (74.8-92.5); hazard ratio (HR) 3.9; 95CI 1.6-9.7; p = 0.003]. When stratified by SOT type, similar trends were seen but were only statistically significant among lung SOT recipients (Table). The 5-year cumulative incidence of primary cancer relapse from time of SOT among those who received liver SOT for primary cancer therapy was 15.9% (95CI 5.6-30.8). Among CAYACS who require SOT following organ toxicity, 10-year cumulative incidence of second cancers was 8.6%±4.2%; this was similar to the incidence of first cancer among SOT controls (6.4%±2.6%; HR 1.6, 95CI 0.6-4.0; p = 0.34). Conclusions: Though CAYACS requiring SOT have inferior survival compared to other SOT patients, the majority achieve long-term cancer-free survival. These data can inform discussions on the suitability of CAYACS for SOT.