The modified Rodnan skin score (mRSS) is a measure of skin thickness and is used as a primary or secondary outcome measure in clinical trials of systemic sclerosis (scleroderma). This state-of-art review provides a historical perspective of the development of the mRSS, summarizes the performance of mRSS as an outcome measure, provides guidance on assessing mRSS, and makes recommendations for incorporation of the mRSS into clinical trials.