Oncology patients undergoing treatment can experience substantial pain related to their disease or prescribed therapy. Ketamine infusions at subanesthetic doses have been used at our institution to supplement the pain management regimens of 262 patients. We present 2 cases in which young adult patients being treated with subanesthetic ketamine for cancer-related pain experienced urinary urgency and incontinence after initiation or increase of the ketamine infusion. This adverse effect has not been reported previously at this dosing range. These case reports suggest that subanesthetic ketamine infusions may cause side effects that previously have been reported only at anesthetic or abuse doses.