OBJECTIVES: To evaluate treatment patterns when different definitions of discontinuation are used. Anti-tumor necrosis factor therapies including adalimumab (ADA), etanercept (ETA) and infliximab (IFX) are used to treat rheumatoid arthritis (RA). Examining discontinuation rates can help understanding of real-world treatment patterns. Different definitions of discontinuation rates have been reported elsewhere. METHODS: Data between 01/2005-06/2006 were extracted from the i3Innovus database. Inclusion criteria were aged ≥18, ≥1 claim for RA, and no evidence of pre-index biologic use in the six months prior.  Patients were followed for 24 months. Discontinuation was defined as a gap in therapy ≥60 or ≥365 days following the last days supply. RESULTS: Total of 1,780 patients were analyzed: ADA= 601 (33.8%); ETA= 785 (44.1%); IFX =394 (22.1%).  If discontinuation was defined as a gap in therapy of ≥60 days, 57.2% of patients treated with ADA discontinued, 57.5% of patients treated with ETA and 37.6% of IFX patients discontinued.  If discontinuation was defined as a gap in therapy of ≥365 days, 22.5% of ADA patients discontinued, 17.3% of ETA patients and 18% of IFX patients discontinued.  Of those defined as ‘discontinuers’ after a gap of therapy of ≥60 days, 49.7 % of ADA patients, 62.1% of ETA patients and 12.8% of IFX patients restarted their index therapy on average 146.8, 146.5, and 302.4 days from the time of defined ‘discontinuation’.  Significantly fewer IFX patients restarted their index therapy (P<0.0001) and the time from defined discontinuation to restart was longer (p<0.0001). CONCLUSIONS: This analysis demonstrates that different discontinuation rates are observed when different definitions of discontinuation are employed.  This may impact the understanding of real-world prescribing patterns.  The data also suggests that patients treated with ADA and ETA experience lengthy gaps in therapy.  Future research is needed to examine gaps in therapy on clinical and health economic outcomes.