Objective:To analyse the clinical and laboratory parameters in patients with SLE according to their age at disease onset a retrospective study was undertaken of 272 Brazilian patients fulfilling the 1982 ARA criteria for SLE who were referred to the University Hospital of Campinas between 1973 - 1992. Methods: The patients were divided into three groups according to their age at disease onset: Group A. under the age of 16 (39 patients); Group B age 17 to 49 (223 patients), Group C over the age of 50 (10 patients). Various clinical and laboratorial parameters were analysed and compared among these groups. Results: There were no significant differences in terms of race, time of disease onset of time of follow-up. Group A had more male patients than Groups B (p < 0.05) of C. Alopecia as an early manifestation, seizures and gastrointestinal involvement were more frequent in Group A (p < 0.05). Raynaud's phenomenon was lower in Group A than in Groups B and C (p < 0.05). Pericarditis was higher in Group C than in Groups A or B (p < 0.05). Nephrotic syndrome was lower in Group C than in Group A (p < 0.05). Positive LE cells were higher in Groups A and C than in Group B (p < 0.05). Anti-DNA antibodies were more prevalent in Group A than in B (p < 0.05). Anti-cardiolipin antibodies were more frequent in adult patients (p < 0.05) (Group B). The mortality rate was higher in Group A than in B or C (p < 0.05). Conclusion: The clinical presentation and course of SLE may be influenced by the age at disease onset. Younger patients showed a poorer prognosis with more seizures, gastrointestinal involvement, nephrotic syndrome, and a higher rate of mortality than the other groups. Group A included more male patients and also exhibited more positive LE cells and anti-DNA antibodies. Raynaud's phenomenon was lower in these young patients. Elderly patients (C) presented more pericarditis and showed mild disease.126603607