The purpose of this study was to determine whether MR findings can correlate disease activity as measured by laboratory markers in ankylosing spondylitis. MR images in 19 patients with ankylosing spondylitis were retrospectively analyzed for cartilage abnormality, periarticular erosion, synovial enhancement, and bone marrow edema. Each MR finding was correlated with laboratory inflammatory markers (erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP)) and the sum of ESR + CRP. Synovial enhancement showed a significant correlation with ESR (r=0.58; p<0.01) and increased activity at bone scan (r=0.74; p<0.005), whereas there was no significant correlation with CRP. A significant correlation was found between ESR + CRP and synovial enhancement (r=0.54; p<0.05). Synovial enhancement was more common when ESR + CRP was greater than 30 (p<0.05). In conclusion, synovial enhancement at MR imaging could correlate disease activity as measured by laboratory inflammatory markers in ankylosing spondylitis.