Amelanotic melanoma often leads to delayed clinical diagnosis because of its wide range of clinical appearances and lack of pigmentation. Misdiagnosis of amelanotic melanoma is also common, particularly when it is located at the foot. We report here a 71-year-old male patient with a 17-year history of type 2 diabetes mellitus who presented with a small ulcer under his fifth metatarsal head, which was previously misdiagnosed as a diabetic foot ulcer. The patient was treated with local wound care and systemic antibiotics without any improvement of the ulcer. Further investigation of the patient in our clinic revealed plantar amelanotic melanoma.