Transrectal ultrasonography is a useful technique for the assessment of sacroiliac osteoarthrosis because of the ventral localisation of lesions. Comparison between the right and left side is essential. Due to the deep localisation of the sacroiliac joints, other imaging modalities have limitations for diagnosing osteoarthrosis. A grading system from 1 to 4 is suggested in order to classify the severity of lesions based on the shape of the articular margins and architecture of the ventral sacroiliac ligament. Abnormal ultrasonographic findings should be correlated with clinical manifestations.