Background: Many cancer patients experience chronic and breakthrough pain necessitating the use of both immediate release (IR) and extended release (ER) opioids. The common strategy in treating chronic cancer pain is using ER opioids with the addition of IR opioids for breakthrough pain. The National Comprehensive Cancer Network recommends IR dosing at 0.1-0.2 times the daily ER dose as needed every 1 hour for breakthrough pain, though data is lacking to validate this recommendation. The aim of this exploratory study was to review the current practice in prescribing IR and ER opioids and the IR/ER ratio used in cancer pain management at one comprehensive cancer center (CCC). Methods: We performed a retrospective chart review of 54 consecutive patients at a CCC over a 6 month period. IR/ER doses, dose adjustments and satisfaction with analgesia were recorded. Adjustments in treatment plans were made based on patients' report of effectiveness and side effects associated with ER and IR opioids. Results: 19 of 54 (35%) patients reported adequate analgesia, with the average daily prescribed IR/ER ratio of 0.6 (range 0 to 3.75). In this group, IR opioids were unchanged during the clinic visit. The ER opioids, on average, were also unchanged, though decreased by 25% and increased by 50% in a few cases over serial clinic visits. Of those patients reporting suboptimal analgesia during the clinic visit (65%), 80% had their ER opioids increased, 6% had IR opioids increased, and 9% had both IR and ER increased. The ER opioids were increased by 40% on average and IR by 11% with the average IR/ER ratio changing from 0.5 (range 0-2) to 0.37 (range 0-1.13). Conclusions: These preliminary data highlight the great variability between patient preferences and clinician decisions in terms of IR/ER opioid ratios. In this retrospective study, analgesia was better in the group using higher IR doses with a higher IR/ER ratio. At the same time, patients with suboptimal analgesia had their ER opioids titrated faster and higher than the IR opioids. More studies are needed to determine best practice in the prescribing of long and short acting opioids for management of chronic cancer pain.