Eruptive vellus hiar cysts(EVHCs) are rare epidermal cysts with vellus hairs that can be inherited or acquired. EVHCs were first identified in 1977, by Esterly et al. and are considered as a developmental anomaly of follicular occlusion. Clinically, small red or brown colored cystic papules usually occur on the chest and proximal extremities. In 1980, Stiefler and Vergfeld reported a hereditary nature for this disorder. Histologically, small cysts are observed in the mid-dermis level and containmultiple hair shafts and keratinous materials. A 40-year-old man with mental retardation had multiple bluish papules on his back which occurred several months ago. There was no family history of a similar disorder. A biopsy specimen from the papule showed a mid-dermal cyst which was filled with cutting vellus hair shafts and keratin materials. These findings were consistent with the diagnosis of EVHC. Herein, we report a case of EVHC that occurred on a patient with mental retardation.