Systemic lupus erythematosus (SLE) is a clinical syndrome of varying severity. Although the survival and prognosis of SLE have steadily improved, there is a group of patients who present an acute fatal outcome despite aggressive therapy. We designed this study to evaluate the factors associated with mortality in patients with acute severe SLE. During 2004-06, 41 Mexican SLE patients that could not be managed in the out-patient clinic and with acute severe major organ system involvement [nephritis, severe thrombocytopenia (platelet count below 20 000 per microL) acute neuropsychiatric pulmonary, gastrointestinal or cardiac disease and generalized vasculitis] were studied. During the first admission, disease activity (SLE Disease Activity Index (SLEDAI), SLE Activity Measured), damage [SLE International Collaborating Clinics (SLICC)], and therapy were assessed. Survival using Kaplan-Meier curves, odd ratios with 95% confidence interval and logistic regression analysis were used to determine risk factors for mortality. Ninety percent were female with a mean age of 29 +/- 19 years and mean disease duration of 21 +/- 9 months. The principal causes of first admission were renal (27%), SNC (22%) and cardiopulmonary (15%). After a mean follow-up of 9.7 +/- 6 months, 16 (39%) patients died. Deceased patients had significantly higher SLEDAI (P = 0.004), and SLICC (P = 0.03) scores. The manifestations associated with mortality were renal disease activity (odds ratio, OR 4.6, confidence interval, CI 95% 1.0-20.6), infections (OR 3.2 CI 95% 2.0-5.3) and thrombocytopenia (OR 4.0, CI 95% 1.0-15.9). The survival at 9.7 months was 72, 62 and 50% in patients with an SLEDAI score of 3-10, 11-20 and > or =21, respectively. The SLEDAI score, the presence of damage and infection were associated with death in patients with acute severe SLE.