Extramammary Paget's disease (EMPD) is a rare cutaneous malignancy involving the scrotum and may be confused with other scrotal malignancy. We describe the sonographic findings of an extremely rare case of mass-forming EMPD of the scrotal wall. Ultrasonography, which shows mild heterogeneous hyperechoic masses with a stalk connected to the dermis, can help predict the depth of vertical invasion of the lesion. The lesion extent should be precisely evaluated because the presence of dermal invasion of EMPD is the risk factor in distant metastasis and is known to result in a worse prognosis. Ultrasonography is a primary imaging modality to evaluate the extent and vertical invasion of EMPD. Surgical local wide excision is the treatment of choice for EMPD and histopathology confirmed the diagnosis.