Introduction: NSAIDS offer more effective analgesia than opioids, require less rescue medication, and decrease the incidence of nausea and vomiting in renal colic patients. Alpha blockers and Opioids are also prescribed frequently, but doses used and treatment durations are not well described. Our objective was to investigate ED prescribing decisions and medication compliance by patients with acute renal colic. Methods: In this prospective two-city cohort study, we invited patients with a first ED visit for image-confirmed 2-10 mm ureteric stones to consent to a telephone survey 10 days after their ED visit. During follow-up interviews, patients were asked what drugs they were prescribed and how many doses they required. This study was REB approved. Results: A convenience sample of 224 patients, including 152 males (67.9%) and 72 females (median age= 52.4 years) completed 10-day surveys. NSAIDS were prescribed for 48.7%, tamsulosin for 65.2% and opioids for 81.7%. One-third received a tamsulosin-NSAID combination, 40% an opioid-NSAID combination and 28% a tamsulosin-NSAID-opioid combination. Of 109 patients prescribed an NSAID, only 70 (64.2%) took 1 dose/day; however an additional 28 who were not prescribed NSAIDs took 1 NSAID dose/day. Mean (sd) NSAID intake in the overall study group was 1.1 (1.5) doses/day from day 1-5 and 0.6 (1.1) doses/day on days 6-10, with 90%ile values of 3.0 and 2.0 doses/day. NSAID compliance was more common in patients who stated they received high quality discharge instructions (63.8% vs. 32.6%; RR=1.95; 95% CI 1.47-2.60). Mean opioid intake in the overall study group was 1.2 (1.7) doses/day from day 1-5 and 0.5 (1.3) doses/day on days 6-10, with 90%ile values of 4.0 and 2.0 doses/day. Among patients prescribed tamsulosin, the average was 4.0 days of compliance (sd=4.3), with a 90%ile value of 10 days. Conclusion: This study provides estimates for the amount of drug actually used by renal colic patients during the 10-days after their ED visit. Patients used fewer opioid doses than expected, and NSAID and tamsulosin compliance appears relatively poor. NSAID compliance was better in patients who perceived high quality discharge instructions. This study suggests there is room for improvement in medication prescribing and discharge instructions for ED patients with an acute episode of ureteral colic.