Objective-To define the pattern of disease expression in patients with childhood onset systemic lupus erythematosus (SLE).Methods-Prospective analysis of clinical manifestations and immunological features of 34 patients in whom the first manifestations appeared in childhood from a series of 430 unselected patients with SLE. Results-Thirty one (91%) patients from the childhood onset group were female and three male (9%) (ratio female/male, 10/1, with no diVerence compared with the adult onset group). Mean age of this group at disease onset was 11 years (range 5-14) compared with 32 years (15-48) for the remaining patients. The childhood onset patients more often had nephropathy (20% v 9% in adult onset SLE, p=0.04; OR:2.7; 95%CI:1.1, 7), fever (41% v 21%, p=0.006; OR:2.6, 95%CI:1.2, 5.7), and lymphadenopathy (6% v 0.5%, p=0.03, OR: 12.3, 95%CI: 1.2, 127.6), as presenting clinical manifestations. During the evolution of the disease, the childhood onset patients had an increased prevalence of malar rash (79% v 51%, p=0.002; OR:3.7; 95%CI:1.5, 9.5) and chorea (9% v 0%, p<0.0001). This group exhibited a higher prevalence of anticardiolipin antibodies (aCL) of the IgG isotype when compared with the remaining patients (29% v 13%, p=0.017; OR:2.9, 95%CI:1.2, 6.8). No significant diVerences were found among the other antibodies between the two groups. Childhood onset patients more often received azathioprine (15% v 6%, p=0.00004; OR:11.2; 95%CI:2.8, 44.9) but no diVerences were detected between the groups concerning side eVects or drug toxicity. Conclusions-The presentation and the clinical course of SLE varied in this series of 430 patients depending on their age at disease onset. Nephropathy, fever, and lymphadenopathy were more common in childhood onset patients as presenting clinical manifestations, while malar rash, chorea, and detection of IgG aCL were more common during the evolution of the disease.(Ann Rheum Dis 1998;57:456-459)