Duloxetine is indicated for the treatment of chemotherapy induced neuropathic pain in adults. It is also indicated for anxiety, depression and fibromyalgia in children. A rare side effect of syndrome of inappropriate antidiuretic hormone (SIADH) secretion has been reported in adults but not in pediatrics or pediatric oncology patients. We present a case of a 10-year-old child with acute lymphoblastic leukemia who developed SIADH after duloxetine was given for chemotherapy-induced neuropathic pain and co-morbid anxiety. The SIADH resolved after duloxetine was stopped. This case highlights a rare side effect of duloxetine and caution should be taken when prescribing duloxetine to children.