Objective: To assess the sensitivity and specificity of detecting subarticular bone erosion of sacroiliac (SI) joint in patients with spondyloarthritis (SpA) using MRI three-dimensional water selective balanced steady-state free precession sequence (3D-WS-bSSFP) and TI-weighted (T1W) sequence. Materials and methods: Radiography, CT and MRI of SI joint from 43 SpA patients were retrospectively analyzed. MRI examination sequences include T1W, short tau inversion recovery (STIR) and 3D-WSbSSFP. Two radiologists, blinded to clinical data, independently determined bone erosion at bilateral sacral and iliac sides of the SI joint on radiography, CT, T1W and 3D-WS-bSSFP respectively. X-2 test was used to compare the sensitivity of detecting bone erosion among different diagnostic methods. Results: Of the 86 sacral and 86 iliac articular surfaces from the 43 cases, radiography, CT, MRI T1W and 3D-WS-bSSFP showed the presence of bone erosion in 40, 74, 50 and 71 articular surfaces respectively. CT and MRI 3D-WS-bSSFP demonstrated similar sensitivity (x(2) =0.11, 13= 0.74), and both were superior to radiography (x(2) =15.17, P< 0.01 and x(2) = 12.78, 13< 0.01, respectively) and T1W (x(2) = 7.26, 13< 0.01 and x(2) = 5.62, P< 0.05). Using CT diagnosis as the gold standard, the sensitivity and specificity of detecting bone erosion for MRI 3D-WS-bSSFP and T1W sequences were 91.8%, 96.9%, and 60.8%, 94.9% respectively. Conclusion: MRI 3D-WS-bSSFP sequence is associated with short scanning time, zero ionizing radiation, high sensitivity and specificity of displaying the subarticular bone erosion of SI joints in patients with SpA. Therefore, it can be considered an alternative to CT. (C) 2014 Elsevier Ireland Ltd. All rights reserved.