Purpose: Patients with IBD on thiopurines have been shown to be at elevated risk of lymphoma from a recent meta-analysis (Kotlyar D, et al 2011 DDW). To date no review has examined the dosage of thiopurine medication in relation to risk of lymphoma. The aim of this study was to examine the relation between dosage of thiopurine medication and risk of lymphoma. Methods: We searched MEDLINE for: “lymphoproliferative and thiopurines”; “thiopurine and lymphoma” and “azathioprine and lymphoma”. Included citations were population based studies examining IBD, evaluated cancer as an outcome, and pts. received AZA and/or 6-MP with dosage information included. In addition, we obtained the primary data from the ENEIDA database, a population based database from Spain. The ENEIDA database is a 3,900 patient national database from Spain with a mean followup time of 9.54 years. From the database patients were divided into three categories: the first were patients taking from 15-99 mg daily, the second from 100-199 mg daily, and the third more than 200 mg daily. Results: Of 606 citations, only 1 citation (Vos, 2011 Inf. Bowel Dis.) included data on dosage in patients with lymphoma in IBD. Among the studies, 1 patient was observed to have developed lymphoma at a dose of 50 mg daily. Nine patients developed lymphoma at doses from 100-199 mg and 1 patient developed lymphoma taking more than 200 mg daily. In the ENEIDA database, we analyzed the primary data and discerned that there were four lymphomas in the 100-199 mg group, and per background rates of lymphoma in Spain, the expected number of lymphomas was 1.98 in this group, whereas the number observed was 4 (SIR=2.02 95% CI: 0.642-4.87). Conclusion: Cases of lymphoma classically occur at doses greater than or equal to 100 mg daily. Only one lymphoma occurred in a patient taking 50 mg a day. Thus, the majority of lymphomas in patients taking AZA/6-MP occur with higher doses. Because of limited dosage data available and the relative rarity of lymphoma in patients with IBD using immunomodulators pooling of additional large population cohort studies are needed. Disclosure: Gary R. Lichtenstein, MD - Abbott Corporation-Consultant; Alaven-Consultant; Bristol-Myers Squibb-Research; Centocor Orthobiotech-Consultant, Research; Elan-Consultant; Ferring-Consultant, Research; Millenium Pharmaceuticals-Consultant; Proctor and Gamble-Consultant, Research; Prometheus Laboratories, Inc.-Consultant, Research; Salix Pharmaceuticals-Consultant, Research; Schering-Plough Corporation-Consultant; Shire Pharmaceuticals-Consultant, Research; UCB-Consultant, Research; Warner Chilcotte-Consultant, Research; Wyeth-Consultant.