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Although adult T-cell leukemia/lymphoma (ATL) has a higher burden in Latin America compared to North American or European countries, few studies have described the outcomes of this disease. We estimated the hospital-based prevalence and overall survival (OS) of ATL. We conducted a cohort study among patients aged ≥ 18 years with pathologically diagnosed mature T-cell lymphoma across 11 Latin American countries from 2000 to 2023 by pooling data from 3 hospital-based registries. We used the Kaplan-Meier method to estimate survival outcomes. Among 1963 patients with mature T-cell lymphoma, the pooled prevalence of ATL was 17 % (n = 329; 95 % confidence interval [CI]=15–18 %), with the highest observed in Peru (n = 158; 38 %, 95 % CI=33–43 %) and Colombia (n = 17; 29 %, 95 % CI=18–41 %). Over time, ATL cases only increased significantly in Peru, from 14 % in 2000–2004 to 58 % in 2019–2023 (Ptrend<0.001). With a median follow-up of 37 months (95 % CI=30–54 months), the 3-year OS of ATL was 25 % (95 % CI=20–32 %), and the median OS was 9 months (95 % CI=8–12 months). OS did not differ across countries (range 19–47 %, P = 0.210). Patients with lymphomatous ATL had worse outcomes than those with PTCL-NOS only in Peru (Pheterogeneity=0.029). Our findings indicate a higher ATL prevalence in Latin America than previously reported in North America or Europe, likely due to differences in HTLV-1 endemicity and diagnostic practices. The similar and poor survival rates across countries underscore the need for targeted interventions to improve patient outcomes. We propose expert-based research priorities and suggest further epidemiological validation studies. •ATL prevalence in Latin America is likely higher than in other regions.•Survival rates for ATL patients remain poor across countries.•Lack of HTLV screening may lead to misdiagnosis of ATL as PTCL-NOS.•Population- based validation studies and expert-based research priorities and are needed to improve outcomes•Collaborative capacity-building will accelerate discovery and enhance ATL-related health outcomes globally