Colouterine fistulae secondary to sigmoid diverticulitis are unusual. Methods for diagnosis remain to be established. We report a case with a colouterine fistula in which sonohysterography detected the flow of ultrasound contrast medium between the uterine cavity and the sigmoid colon through the posterior uterine wall, thus confirming the diagnosis. The diagnosis was further substantiated by a charcoal challenge test. The patient underwent en bloc resection of the uterus, Fallopian tubes, ovaries and sigmoid colon, the organs involved with diverticulitis. This is the first report to describe a colouterine fistula successfully diagnosed by sonohysterography using ultrasound contrast medium. Copyright © 2004 ISUOG. Published by John Wiley & Sons, Ltd.