Objective. The outcome of patients with recent-onset spondylarthropathy (SpA) is unclear. Therefore, the objective of this study was to prospectively correlate clinical and laboratory features with functional and radiologic outcome in patients with psoriatic SpA (PsS), undifferentiated SpA (uSpA), and Reiter's syndrome/reactive arthritis (ReA). Methods. Patients presenting to an early arthritis clinic with a spondylarthropathy pattern of peripheral arthritis were selected and prospectively followed. Clinical and laboratory features were recorded at baseline, 12 months, and 24 months. Radiographs of affected joints were taken at presentation and at followup. Results. The cohort consisted of 157 patients: 82 PsS, 59 uSpA, and 16 ReA. Symptom duration at presentation was progressively shorter, and the erythrocyte sedimentation rate/C-reactive protein (ESR/CRP) incrementally higher in ReA, uSpA, and PsS, respectively. There was a higher swollen joint count (SJC) in PsS compared with uSpA. In PsS, strong positive correlations were observed between ESR/CRP and articular indices. Initially, functional impairment was greater in ReA compared with uSpA and PsS but resolved completely in ReA. Clinical remission rates at 2 years were ReA 61% and uSpA 63%, compared with PsS 14%. Remission at 2 years could be predicted in SpA by disease category and presentation SJC. Baseline erosions in PsS (28%) and uSpA (5%) increased to 45% and 25%, respectively, at 2 years. Conclusion. These observations suggest a spectrum within the spondylarthropathy subgroups where at presentation the acute phase markers in ReA and uSpA reflect a systemic process, whereas in PsS they reflect articular manifestations. Although the clinical presentations are indistinguishable, PsS has a more aggressive clinical course with a poorer functional and radiologic outcome.