Objective: To investigate the efficacy of 16-week treatment with etanercept (ETN) in patients with suspected nonradiographic axial spondyloarthritis (SpA). Methods: Tumor necrosis factor inhibitor–naive patients with inflammatory back pain with at least 2 SpA features and high disease activity (Bath Ankylosing Spondylitis Disease Activity Index score ≥4), without the requirement of a positive finding on magnetic resonance imaging (MRI) of the sacroiliac (SI) joint and/or elevated C-reactive protein (CRP) level, were randomized (1:1) to receive ETN (n = 40) or placebo (n = 40) for 16 weeks and subsequently were followed up for a further 8 weeks (to 24 weeks from baseline) without study medication. The primary end point was the Assessment of SpondyloArthritis international Society 20 (ASAS20) response at 16 weeks. Secondary end points included the Ankylosing Spondylitis Disease Activity Score (ASDAS) and changes in disease parameters, including the Bath Ankylosing Spondylitis Metrology Index (BASMI), CRP level, erythrocyte sedimentation rate (ESR), and Spondyloarthritis Research Consortium of Canada index scores (MRI of the SI joint), after 16 and 24 weeks. Results: Patient characteristics at baseline were comparable between the ETN and placebo groups. At 16 weeks, there was no significant difference in the percentage of patients exhibiting ASAS20 response between the ETN group (6 patients [16.7%]) and the placebo group (4 patients [11.1%]) (relative risk 0.7 [95% confidence interval 0.2–2.2], P = 0.5). Only the ESR showed more improvement in the ETN group compared to the placebo group at 16 weeks (decreases of 2.2 mm/hour and 1.4 mm/hour, respectively), but the difference did not reach statistical significance. Between 16 and 24 weeks, without study medication, the BASMI, CRP level, and ESR had worsened to a greater extent in the ETN group compared to the placebo group, with the difference being significant for the CRP level. Conclusion: This study shows that in patients with suspected nonradiographic axial SpA with high disease activity but without the requirement of a positive finding on SI joint MRI and/or elevated CRP level, treatment with ETN is not effective.