Opioids remain the most commonly used, and most commonly recommended, treatment for acute undifferentiated abdominal pain (UAP). There are a number of RCTs (with placebo controls) addressing morphine use for UAP, including pain suspected to be from appendicitis. The evidence clearly and consistently demonstrates safety and efficacy from morphine use in the UAP population. The use of fentanyl is theoretically attractive, since this agent has a short duration of action and is therefore easier to titrate. Both morphine and oxycodone (PO) have been specifically studied in children with UAP. The mixed-mechanism agent tramadol, administered IV, has been found efficacious for UAP in one clinical trial. Use of NSAIDs is likely to help to alleviate any pain from stone movement. There is also evidence basis for COX-2 inhibition as a means to moderate pain from pelvic inflammatory disease.