The sacroiliac (SI) joints of 45 asymptomatic subjects were prospectively studied to define better the normal appearance of SI joints on CT scans and thereby attach appropriate significance to CT signs of sacroiliitis. We evaluated joint space narrowing, subchondral sclerosis, erosions, ankylosis, osteophytes, subchondral cysts, and symmetry. The results indicate that the SI joints demonstrate symmetry in patients under the age of 30 (100% of subjects in this age group). Asymmetry was demonstrated in 77% of subjects over the age of 30 and in 87% of subjects over the age of 40. Abnormal CT findings of sacroiliitis, which occurred frequently in the asymptomatic population and thus by themselves are believed to be poor indicators of sacroiliitis, include nonuniform iliac sclerosis (83%), focal joint space narrowing in patients over the age of 30 (74%), and ill-defined areas of subchondral sclerosis, particularly on the iliac side (67%). Those CT findings of sacroiliitis that occurred infrequently in the asymptomatic population, and hence may represent good indicators of sacroiliac disease, include increased sacral subchondral sclerosis in subjects under the age of 40 (11%), bilateral or unilateral uniform joint space of less than 2 mm (2% or 0%, respectively), erosions (2%), and intraarticular ankylosis (0%).