Potassium-binding resins are widely used in the treatment of hyperkalemia, mostly in the acute setting. Gastrointestinal adverse events, although reported, are not frequently seen due to its short course of use. This report describes a case involving an end-stage renal disease patient on hemodialysis who developed a colonic mass after being on sodium polystyrene sulfonate chronically for persistent hyperkalemia. Gastrointestinal symptoms developed late during the treatment rather than early as reported previously in the literature. This mass was mistaken for a carcinomatous lesion, which initiated an extensive work-up as well as hospitalization that nearly resulted in a subtotal colectomy.