CONTEXT AND OBJECTIVE: Systemic lupus erythematosus is a chronic disease that is more frequent in women of reproductive age. The relationship between lupus and pregnancy is problematic: maternal and fetal outcomes are worse than in the general population, and the management of flare-ups is difficult during this period. The aim here was to compare the outcomes of 76 pregnancies in 67 women with lupus, according to the occurrence or absence of flare-ups. DESIGN AND SETTING: An observational cohort clinical study evaluating the evolution of pregnant women with lupus who were receiving care at the prenatal outpatient clinic, Centro de Atenção Integral à Saúde da Mulher, Universidade Estadual de Campinas (CAISM/Unicamp), between 1995 and 2002. METHODS: Data were collected on a precoded form. The women were divided into two groups according to the occurrence or absence of flare-ups, as defined by the systemic lupus erythematosus disease activity index (SLEDAI). The presence or absence of flare-ups and renal involvement was considered to be the independent variable and the other results were dependent variables. RESULTS: Flare-ups occurred in 85.3% of cases, and were most significant when there was renal involvement. This was related to greater numbers of women with preeclampsia and poor perinatal outcome. Intrauterine growth restriction was more common in the women with active disease. Placental weight was significantly lower in the women with renal involvement. CONCLUSIONS: Flare-ups and renal involvement in lupus patients during pregnancy are associated with increased maternal and perinatal complications.