Idiopathic hair casts are described in two girls aged 5 and 7 years. A 0.025% tretinoin lotion seemed effective in removing the casts. Investigations, including light microscopy and transmission electron microscopy, suggest an infrainfundibular origin for these lesions, because both inner and outer root sheath components were observed in the transverse sections of the casts. A comprehensive review of the literature enabled us to classify the patients into two distinct groups: group 1 consisted of patients with idiopathic disease, showing a diffuse pattern of involvement, and group 2 consisted of patients with disease secondary to a variety of inflammatory scalp disorders.