Background COMPLETE-AS is an ongoing Canadian observational study of anti-TNFα naïve adults with active AS per the judgment of the treating physician, who require change in current AS treatment to either1 a subsequent NSAID or non-biologic disease modifying antirheumatic drug (nbDMARD group), or2 to adalimumab (ADA group). Objectives The aim of this analysis was to describe and compare the baseline demographic and disease parameters of patients in the nbDMARD and ADA groups and to compare the 12 month effectiveness of the two treatment methods. Methods In the current analysis patients enrolled between July/2011 – Jun/2016 were included. Outcome measures analysed were extra articular manifestations (EAM 1: IBD, psoriasis, uveitis, enthesitis; EAM 2: IBD, uveitis, enthesitis), disease activity (BASDAI), functional status (BASFI), and quality of life (QoL; SF-12). Between-group differences in baseline parameters were assessed with the Chi-square test for categorical variables and the independent samples t-test for continuous variables. Baseline-adjusted changes in BASDAI and BASFI over time were compared between the two groups using linear mixed models. Results A total of 609 patients (nbDMARD n=177, ADA n=432) were included in the current analysis. No significant differences in baseline demographics were observed between the two groups. However, at baseline, patients initiating ADA were more likely to be unemployed (38% ADA vs. 27.1% nbDMARD, p=0.009), had higher mean BASDAI (6.4 vs. 5.0; p<0.001) and BASFI (5.5 vs. 3.7; p<0.001) scores, and worse QoL (SF-12 PCS: 24.4 vs. 24.7, p=0.002) at baseline. The baseline prevalence of EAMs was comparable between the two groups (EAM 1: 34.7% vs. 31.6%, p=0.454; EAM 2: 25.9% vs. 22.6%, p=0.381). However, IBD was more common among patients initiating ADA treatment (9% vs. 4.5%, p=0.062). After 12 months of treatment the prevalence of EAMs decreased significantly in the ADA group (EAM 1: p=0.004; EAM 2: p=0.033) but not in the nbDMARD group. After adjusting for baseline values, patients treated with ADA had numerically lower BASDAI score (least square means – LSM: 3.7 vs. 4.3, p=0.171) significantly lower BASFI score (2.9 vs. 3.6, p=0.031) scores, and comparable SF12-PCS (24.9 vs. 24.7, p=0.210) and SF12-MCS (19.1 vs. 18.9, p=0.532) scores at 12 months. During follow-up, 7.4% of ADA patients initiated another biologic and 23.7% of patients in the nbDMARD group initiated biologic treatment (p<0.001). Conclusions AS patients initiating ADA in Canadian routine clinical care have significantly greater disease severity and impaired quality of life at baseline compared with those initiating non-biologic treatment. Treatment with ADA for 12 months resulted in greater reduction in the prevalence of EAMs and a greater reduction in disease severity scores compared to treatment with non-biologic agents. Acknowledgements JSS Medical Research, Montreal, Canada Disclosure of Interest L. Bessette Consultant for: Amgen, BMS, Janssen, Roche, UCB, AbbVie, Pfizer, Celgene, Lilly, Novartis, Speakers bureau: Amgen, BMS, Janssen, Roche, UCB, AbbVie, Pfizer, Merck, Celgene, Lilly, Novartis, M. Khraishi Consultant for: AbbVie, Speakers bureau: AbbVie, A. Chow Consultant for: AbbVie, Amgen, BMS, Celgene, Janssen, Lilly, Merck, Novartis, Pfizer, Roche, Speakers bureau: AbbVie, BMS, Janssen, Pfizer, Takeda, V. Pavlova Grant/research support from: UCB, Consultant for: Amgen, Abbvie, BMS, Janssen, Lilly, Merk, Novartis, Roche, UCB, Pfizer, Speakers bureau: Amgen, Abbvie, BMS, Janssen, Lilly, Merk, Novartis, Roche, UCB, Pfizer, S. Silverberg Consultant for: AbbVie, Janssen, J. Stewart Consultant for: Pfizer, Abbvie, Amgen, Celgene, Roche, Novartis, V. Remple Shareholder of: AbbVie, Employee of: AbbVie