OBJECTIVES: To describe the frequency and types of disease damage occurring with childhood-onset systemic lupus erythematosus (cSLE) as measured by the 41-item Systemic Lupus International Collaborating Clinics/American College of Rheumatology Damage Index (SDI), and to assess the SDI's ability to reflect damage severity. METHODS: Information for the SDI was prospectively collected from 1,048 cSLE patients. For a subset of 559 patients physician-rated damage severity measured by visual analog scale (MD-VASdamage ) was also available. Frequency of SDI-items, and the association between SDI summary-scores and MD-VASdamage were estimated. Finally, an international consensus conference, utilizing nominal group technique, considered the SDI's capture of cSLE-associated damage and its severity. RESULTS: After a mean disease duration of 3.8 years, 44.2% (463/1048) of patients already had an SDI summary-score >0 (maximum: 14). The most common SDI items scored were proteinuria, scarring alopecia, and cognitive impairment. Although there was a moderately strong association between SDI summary-scores and MD-VASdamage (rSpearman = 0.49; p<0.0001) in patients with damage (SDI summary-score >0), mixed effect analysis revealed that only four SDI items, each occurring in <2% of patients overall, were significantly associated with MD-VASdamage . There was consensus among cSLE experts that the SDI in its current form is inadequate for estimating the severity of cSLE-associated damage. CONCLUSION: Disease damage as measured by the SDI is common in cSLE, even with relatively short disease durations. Given the shortcomings of the SDI, there is a need to develop new tools to estimate the impact of cSLE-associated damage. This article is protected by copyright. All rights reserved.