Case report Open Access Published: 25 April 2022 Journal of Medical Case Reports volume 16, Article number: 163 (2022) Cite this article Abstract Background Capecitabine is widely used in chemotherapy for breast, colorectal, and gastric cancers. The frequent adverse reactions of capecitabine mainly include gastrointestinal side effects, anemia, and cardiovascular toxicity. Here, we report a rare case of severe hyperglycemia and hypokalemia during long-term treatment with capecitabine.