Pralsetinib is a rearrangement during transfection (RET) selective tyrosine kinase inhibitor (TKI) approved for treatment of metastatic nonsmall cell lung cancer (NSCLC) with RET-fusion and advanced/metastatic radioiodine-refractory thyroid carcinoma with RET-fusion.1 Although considered effective and safe in its treatment of these cancers, it is commonly associated with gastrointestinal (GI) treatment-related adverse events (TRAE).1–3 We report a unique case of pralsetinib-induced lymphocytic colitis (LC) in a patient treated for stage 3c NSCLC. This evidence concerns the gene RET and lymphocytic colitis.