Background: Assessment of severity is essential in the clinical care of rosacea patients and in the research on rosacea. Objective: To determine the range of methods used to assess rosacea severity in clinical trials. Methods: The medical literature from 1965 through 2001 was searched for rosacea clinical trials using MEDLINE and published citations. Forty-seven articles were reviewed. Results: The most frequently assessed signs of rosacea were papules/pustules (43 studies), erythema (35), and telangiectasia (24). Other signs and symptoms of rosacea and adverse reactions to therapies were assessed in 27 studies. Counts of papules/pustules were conducted in 34 studies. Four-point scales were the most frequently used assessment tools for erythema (17) and telangiectasia (11). Other frequently used techniques included global assessment by clinicians (29) and by patients (21), and photography (13). Conclusions: At present, there are no standard validated tools for assessing the severity of rosacea or its signs or symptoms.