Skin involvement is a frequent presenting manifestation of systemic lupus erythematosus (SLE). Cutaneous lupus erythematosus (CLE), frequently occurring without SLE, may be even more common than SLE. Until recently, clinical instruments to measure skin involvement in CLE did not exist, hampering clinical research in this field. In this paper the present authors describe outcome instruments for SLE and outline the considerations underlying the design and validation of an outcome instrument for CLE, the cutaneous lupus disease area and severity index. These studies serve as a model for development and validation of standardized instruments that can be applied to other cutaneous diseases, particularly autoimmune diseases, in order to facilitate epidemiologic studies and clinical trials.