Five immunosuppressed patients with neutropenic typhlitis were studied with sonography. In four, sonography was the imaging technique that first suggested the diagnosis. In each case, sonography showed thickening of the right colon wall (1-2.5 cm) with low- or high-level echoes. Serial sonograms were used to monitor the daily progress of the disease in two patients. Sonography appears to be a useful tool not only to detect typhlitis in patients with symptoms suggestive of the disease, but also to follow their clinical course.