Methods for scoring the severity of radiological change in patients with ankylosing spondylitis using plain X-rays of the sacroiliac (SI) joints and lumbar spine and computerized tomographic (CT) scans of the SI joints were evaluated in a cohort of 70 patients. Analysis of reproducibility was by the kappa statistic. Significant change over 12 months in a subgroup of patients was demonstrated by these scores. Ankylosis correlates negatively with erosions and sclerosis and the change in SI joint ankylosis correlates negatively with change in SI joint erosions as seen on CT scan. The clinical and laboratory correlates of these findings were examined. Pain, stiffness and sleep disturbance correlated positively with increasing SI joint sclerosis on CT scanning (r = 0.45; P less than 0.05) but negatively with ankylosis (r = -0.43; P less than 0.05). Orosomucoid levels predicted an increase in the radiological lumbar spine score. No other clinical or laboratory variable predicted radiological change.