This retrospective cohort study examined the association between radiotherapy and prognosis in follicular lymphoma (FL) patients, with stratification by age, Ann Arbor stage, primary tumor site, surgical status, and grade. Using data from the SEER database, we employed Cox proportional hazards and competing risk models to assess the impact of radiotherapy on overall survival (OS) and cancer-specific survival (CSS) in 7,551 FL patients. The association between radiotherapy and second primary cancer (SPC) was explored using Logistic regression model. At the end of the 60-month follow-up, 6,053 patients were alive, while 1,498 had died. The overall result showed that radiotherapy was associated with the better OS [hazard ratio (HR): 0.70, 95% confidence interval (95%CI): 0.59-0.83, P < 0.001] and CSS (HR: 0.67, 95% CI: 0.52-0.87, P = 0.002)) in FL patients. Radiotherapy was associated with improved OS and CSS in patients aged >= 60 years [OS: HR: 0.65, CI: 0.53-0.79; CSS: HR: 0.63, CI: 0.52-0.77], early Ann Arbor stage (OS HR: 0.51, CI: 0.40-0.65; CSS HR: 0.51, CI: 0.40-0.65), primary sites at lymph nodes (OS HR: 0.76, CI: 0.62-0.93; CSS HR: 0.76, CI: 0.62-0.93) and skin/soft tissue (OS HR: 0.35, CI: 0.16-0.81; CSS HR: 0.36, CI: 0.16-0.82), and in both surgical (OS HR: 0.70, CI: 0.52-0.93; CSS HR: 0.70, CI: 0.52-0.93) and non-surgical patients (OS HR: 0.71, CI: 0.56-0.89; CSS HR: 0.69, CI: 0.55-0.87). Radiotherapy showed no significant association with second primary cancer (SPC) risk. These findings suggest radiotherapy improves 5-year survival outcomes in FL patients during the rituximab era.