<h4>Background</h4>This study assessed the safety and effectiveness of selpercatinib, a selective rearranged during transfection (RET) kinase inhibitor, in patients with RET fusion-positive non-small cell lung cancer (NSCLC) in real-world clinical practice in Japan.<h4>Methods</h4>This single-arm, multicenter, prospective observational study included patients with RET fusion-positive NSCLC who received at least one dose of selpercatinib between February 2022 and October 2023. The gene discussed is RET; the disease is non-small cell lung carcinoma.