The objective of this study was to evaluate the predictive factors for achieving partial remission (PR) in patients with ankylosing spondylitis (AS) treated with anti-TNFα. We longitudinally enrolled in a multi-center study 214 AS patients, classified according to New York criteria, treated with anti-TNFα drugs adalimumab (ADA), etanercept (ETA) and infliximab (INF) with at least 12 months of follow up. PR was reached when the score was <20 mm (on a visual analogue scale of 0-100 mm) in each of the following 4 domains: 1) patient global assessment (in the last week); 2) pain (spinal pain); 3) function [measured by the bath ankylosing spondylitis functional index (BASFI)]; 4) inflammation [mean of intensity and duration of morning stiffness, from the bath ankylosing spondylitis disease activity index (BASDAI)]. Two hundred fourteen AS patients (M/F=160/54; median age/range=43.2/19-78 years; median disease duration/ range=96/36-189 months) were treated with ADA (15.8%), ETA (28.9%) and INF (55.1%). At 12 and 24 months, high serum level of C reactive protein (CRP) (≥2 vs ≤0.8 mg/dL) were associated with higher rate of PR in AS patients treated with anti-TNFα drugs. At 24 months, PR was associated with shorter disease duration (≤36 vs ≥189 months) and higher erythrosedimentation rate (ESR) values (≥45 vs ≤17 mm/h). In male patients lower bath ankylosing spondylitis metrology index (BASMI) (≤2 vs ≥6) and absence of psoriasis were associated with higher PR rate only at 12 months. Other parameters assessed before treatment, such as BASDAI, BASFI, peripheral arthritis, inflammatory bowel disease and uveitis were not associated with PR. Our long-term longitudinal study in a setting of clinical practice showed that inflammatory parameters (i.e. CRP, ESR) and disease duration represent the most important predictive variables to achieve PR with an anti-TNFα treatment.