Hypoechogenicity within the myometrium may be considered as uterine fibroids, limited adenomyosis or endometrial cancer. 1. Uterine fibroids: they are the most common benign tumors of the female genitalia and are classified into intermural, subplasma and submucosal fibroids according to their growth sites. Among them, intermural fibroids are the most common ones, which are characterized by single or multiple hypoechoic nodules with clear boundaries in ultrasonography. Subplasma leiomyoma is characterized by hypoechoic nodules protruding from the surface of the uterus, with clitoris attached to the uterus. Submucosal fibroids are generally characterized by hypoechoic or moderately echogenic masses located in the uterine cavity. 2. Restricted adenomyosis: in ultrasonography, it is manifested as enlarged uterus, abnormal nodular echogenicity within the uterine wall, unclear boundary, uneven low or medium echogenicity, and some lesions can be seen as small fluid area. 3. Endometrial cancer: there is no ultrasonographic manifestation in early stage, but in middle and late stage, irregular enlargement of uterus can be seen, and when the lesion invades tissues around the plasma membrane layer, the uterus can be seen to be blurred in contour and poorly demarcated; in middle and late stage, the endometrial cancer can be seen to be endometrial thickening, which can present as focal or diffuse, inhomogeneous medium-low or low mixed or low echogenicity; and in case of invasion of the myometrial layer, hypoechoicity within the myometrium can be found. When hyperechoic myometrium is detected, one should consult a specialized physician for a definite diagnosis.