Abstract Objective To investigate which factors are associated with treatment intensification (TI) in axial spondylarthritis (axSpA) patients with high disease activity (HDA). Methods Patients with axSpA and HDA (Ankylosing Spondylitis Disease Activity Score [ASDAS]≥2.1) from the Dutch SpA-Net registry were included. TI was defined as: 1) higher dose or shorter interval of the same drug, 2) switch from current drug to another due to inefficacy, or 3) addition of a new drug. Only anti-inflammatory drugs were considered. Primary determinants considered were ASDAS, Assessment of SpondyloArthritis international Society Health Index (ASAS HI) and physician global (PhGA). Acceptable symptom state according to patient (PASS-patient) or physician (PASS-physician) were included in sensitivity analyses. Patient-centered and physician-centered logistic regression models were used to investigate the association between potential determinants and TI. Results In total, 121 patients with HDA were included. TI was conducted in a minority (41/121, 33.9%), and mainly involved a switch or addition of a drug. In multivariable regression analyses, a higher ASDAS was associated with TI in the patient-centered model (ORASDAS = 1.94, [95%CI 1.00–3.74]). However, in the physician-centered model, this association attenuated, and PhGA or PASS-physician were the primary factors associated with TI (ORPhGA = 1.71 [1.24–2.34]; ORPASS-physician = 94.95). Interestingly, patient-centered factors (ASAS HI/PASS-patient/education level) did not contribute to TI. Conclusion In practice, treatment is intensified in a minority of axSpA patients with HDA. Physician-centered factors are associated with the decision to change treatment, independently of disease activity or patient perspective. Further research is needed to better understand these decisions.