OBJECTIVES To investigate the association between serum golimumab (GLM) trough levels, clinical disease activity and treatment response during the first year of therapy in patients with axial spondyloarthritis (axSpA), as well as determining an optimal concentration range of GLM in axSpA. METHODS This was an observational prospective study including 49 patients with axSpA monitored during 52 weeks (W52). Serum GLM trough levels were measured by capture ELISA and antidrug antibodies by bridging ELISA at baseline, W24 and W52. Disease activity was assessed by the Ankylosing Spondylitis Disease Activity Score (ASDAS) and clinical improvement by ΔASDAS. The association between serum GLM trough levels and disease activity was assessed using univariable and multivariable regression. In case of drop-out or missing data before W52, the last observation carried forward (LOCF) was performed. ASDAS values and GLM levels at W24 were available for 42 patients and 38 patients at W52. RESULTS In the univariable analyses, serum GLM trough levels were inversely associated with ASDAS at W24 (n=42, r =-0.445; p<0.01), at W52 (n=38, r=-0.330; p<0.05) and W52LOCF (n=49, r=-0.309; p<0.05). In the multivariable analysis, this significant association remained. Serum trough GLM levels above the 0.7-1.4mg/L range did not contribute to additional clinical improvement. CONCLUSIONS In patients with axSpA, serum GLM trough levels are associated with disease activity during the first year of treatment. A concentration range of 0.7-1.4mg/L appears to be useful to achieve clinical response to GLM.