The disease severity instruments for pemphigus and BP, the Pemphigus Disease Area Index (PDAI) and the Bullous Pemphigoid Disease Area Index (BPDAI), respectively, have the potential to capture changes in all grades of disease activity, including mild disease, and therefore represent a substantial improvement over simple lesion counts or measurements of affected body surface area. However, full validation of the PDAI and BPDAI for use in clinical trials will require additional and more extensive measurements that will enable us to classify patients correctly by disease severity and define the minimal change in score that is clinically significant.