• Four children of two kindred had alopecia associated with severe rickets, resistant to treatment, and caused by defective cytoplasmic and nuclear receptors for the active vitamin D metabolite calcitriol (1,25-dihydroxyvitamin D3). Scalp biopsy specimen revealed a normal number and light microscopic features of the hair and hair follicles. Calcitriol-resistant rickets should be added to the list of inherited disorders of hair growth, and the association of rickets with alopecia needs to be considered in the differential diagnosis of hair loss. (Arch Dermatol1985;121:646-647)