Systematic study of 143 patients with primary gout revealed 24 with roentgenographic changes at the sacroiliac joints attributable to the gout. Two of them gave histories suggestive of acute attacks of sacroiliac gout. All patients with sacroiliac gout had tophi and they had earlier onset, longer duration, a more rapid course into chronicity and lower creatinine clearance than those patients without sacroiliac involvement. The roentgenographic features included sclerosis and irregularity of margins, focal osteoporosis and sclerosis-rimmed cysts. Because most patients had not received previous adequate treatment, our finding of sacroiliac involvement in 16.8 per cent of patients probably reflects its true prevalence in gout left to its natural course.