ObjectiveThe goal was to develop and validate classification criteria for axial juvenile spondyloarthritis (SpA; AxJSpA).MethodsThis international initiative consisted of four phases: (1) item generation, (2) item reduction, (3) criteria development, and (4) validation of the AxJSpA criteria by an independent team of experts in an internationally representative validation cohort.ResultsThese criteria are intended to be used on youth with a physician diagnosis of juvenile SpA and for whom axial disease is suspected. Item generation consisted of a systematic literature review and a free‐listing exercise using input from international physicians, which collectively resulted in 108 items. After the item reduction exercise and expert panel input, 37 items remained for further consideration. The final AxJSpA criteria domains included the following: imaging of active inflammation, imaging of structural lesions, pain chronicity, pain pattern, pain location, stiffness, and genetics. The most heavily weighted domains were active inflammation and structural lesions on imaging. Imaging typical of sacroiliitis was deemed necessary, but not sufficient, to classify a youth with AxJSpA. The threshold for classification of AxJSpA was a score of ≥55 (out of 100). When tested in the validation data set, the final criteria had a specificity of 97.5% (95% confidence interval [CI] 91.4%–99.7%), sensitivity of 64.3% (95% CI 54.9%–73.1%), and area under the receiver operating characteristic curve of 0.81 (95% CI 0.76%–0.86%).ConclusionThe new AxJSpA classification criteria require an entry criterion and a physician diagnosis of juvenile SpA and include seven weighted domains. The AxJSpA classification criteria are validated and designed to identify participants for research studies.image