We present a case of late-onset chronic severe painless diarrhea in an 80-year-old man with type 2 diabetes who was on metformin for 5 years. He underwent multiple laboratory and imaging investigations with no underlying cause found. After detailed medication review, a trial of metformin discontinuation resulted in immediate resolution of symptoms. This case highlights the importance of considering metformin as a cause of new-onset diarrhea in patients even if they had previously tolerated the drug well for years, as its discontinuation can potentially prevent patient inconvenience and discomfort associated with unnecessary investigations.