OBJECTIVES: Compare two different formats—checklist and open text— of questions soliciting opioid-related side effects (OSEs) with respect to the proportion of patients reporting OSEs and the number of OSEs reported. METHODS: Data from Day 3 assessment of the oxycodone IR users registry (OUR), an ongoing, prospective, multicenter registry of patients age 18-85 with acute episodes of non-malignant pain requiring treatment with oxycodone IR for >5 days were used. Patients who completed two types of OSEs assessments on Day3 were included in the analysis. The first assessment is in an open-text format allowing for identification of up to 7 symptoms. The second is in a checklist format listing 14 symptoms along with questions about the frequency and degree of distress associated with each. Correspondences between patient responses solicited through the two different formats were examined using descriptive statistics. Interim data were used for the current analysis. The entire registry patient population will be analyzed in early 2010. RESULTS: Among 182 patients examined for this analysis, mean (±SD) age was 49.3 (±12.7) years, 60.2% were female and 74.3% white. Oxycodone IR was most commonly prescribed for injury/trauma (30.5%), back/neck pain (28.8%), and arthritis (18.1%). The proportion of patients reporting any OSEs in the checklist was nearly two-fold that in the open text (98.9 vs 53.6%; p<0.001). Patients, on average, reported 4.1 (SD=6.3) OSEs on the checklist vs 1.3 (SD=1.6) on the open-text question (p<0.001). Significantly more events were reported in the checklist vs open text question for each OSE examined (p<0.001). OSEs reported to be frequent and bothersome on the checklist were significantly more likely to appear in the open text compared to infrequent and mild symptoms. CONCLUSIONS: Frequency and extent of OSE reporting may vary by the format of questions administered. Caution is warranted in collecting, reporting, and comparing symptom data from different studies.