Epidermal inclusion cyst is one of the common benign soft tissue tumors, and it can be easily confirmed and treated by surgical excision. We experienced a patient who had multiple masses on the face and scalp region, and the masses had been misdiagnosed as neurofibromatosis because of accompanying mental retardation. We would like to introduce a case of clinical diagnosis error caused by the lack of radiologic evaluation and pathologic confirmation. A 27-year-old male patient visited with multiple masses, with a length of approximately 1 to 10 cm on the face and scalp region. These mass have developed since childhood without known etiology, and there has been no histologic examination or surgical excision done in the past. The patient's history of seizure disorder and mental retardation led the primary clinician to diagnose it as neurofibromatosis in the initial stage, and therefore, the clinician gave an advice on the possibility of frequent recurrence to the patient. As the masses increased in size, the patient came to our hospital after all. We found that the masses were soft and mobile through the physical examination, and magnetic resonance imaging showed evidence of epidermal inclusion cyst, which is distinguished from neurofibromatosis. Based on physical examination and magnetic resonance imaging, we performed total excision and biopsies. On the histologic examination, it was diagnosed as an epidermal inclusion cyst showing keratotic material internally, and the cyst wall was composed of lamellate keratin. The follow-up period was 12 months, and a recurrence has not occurred. The wound was healed without any specific complication, and both the patient and the guardian were satisfied with the physical enhancement. We have observed a misdiagnosed case that was misconceived by the situation, accompanying mental retardation. Due to this misconception, any surgical treatment was not performed at all, and the symptoms eventually worsened as multiple huge epidermal inclusion cysts. We present this case with a brief review of literature.