Primary malignant melanoma of the duodenum is an unusual oncologic entity. Patients usually present the similar clinical symptoms like other common tumors in this site. And there are no specific radiological features either. The cases with only little melanin pigment or without notable melanin pigment are very misleading, especially in small biopsies or frozen sections. Definite diagnosis depends on both careful histologic examination and the use of proper immunohistochemical stains. Moreover, detailed history and thorough investigation should be made to exclude the preexistence or coexistence of a primary lesion elsewhere. Herein we report the case of a 60-year-old male patient with primary malignant melanoma of the duodenum, which was misdiagnosed as lymphoma or undifferentiated carcinoma in frozen consultation. The patient had achieved disease-free survival for more than 46 months without any evidence of recurrence after surgery.