Chronic constipation is a disorder frequently encountered in clinical practice. Here, we describe the use of ultrasonography as a new approach to the follow-up of adult patients with functional chronic constipation. Specifically, we report two cases of functional chronic constipation: fecal retention in the rectum and not fecal retention in the rectum. In the not fecal retention in the rectum patient, ultrasonography showed no evidence of fecal retention in the rectum, including no rectal fecaloma, whereas in the fecal retention in the rectum patient, fecal retention in the rectum was clearly recognized. Moreover, ultrasonography can guide the choice of laxative, enema, or appropriate manual maneuver to treat chronic constipation. As a simple and noninvasive method for assessing functional chronic constipation in adults, ultrasonography not only provides important clinical information but can also aid in determining the location of fecal retention.