The antiphospholipid syndrome is usually defined by the association of a clinical manifestation (recurrent venous and/or arterial thrombosis, recurrent spontaneous miscarriages) and a biological abnormality (anticardiolipin antibody, lupus anticoagulant). We retrospectively analyzed the records of 5 patients (4 females, 1 male, aged 30 +/- 12 years) with antiphospholipid syndrome, primary (n = 1) or secondary to systemic lupus erythematosus (n = 4), who developed malignant systemic hypertension with renal insufficiency, in the absence of lupus nephritis. Before the episode of malignant hypertension, all patients had normal systemic blood pressure and renal function. During malignant hypertension the systolic pressure was 206 +/- 39 mmHg and the diastolic pressure 130 +/- 25 mmHg, peak serum creatinine was 204 +/- 95 mumol/l, daily proteinuria was 1.1 +/- 0.8 gr, and complement serum levels were normal in all patients. Renal angiography found normal proximal renal arteries. Renal biopsy showed ischaemic glomeruli without proliferative lesions (n = 5), focal intimal fibrosis either isolated (n = 3) or associated with thrombosis (n = 2) of the intrarenal vessels, and the absence of vasculitis. Immunofluorescence study did not reveal typical lupus deposits. Patients were treated with antihypertensive agents, increasing doses of prednisone (n = 3), and anticoagulant (n = 2) or anti-aggregant therapy (n = 1). After a mean follow-up of 6.8 +/- 5.2 years, 4 patients were still alive with normal blood pressure and renal function, whereas 1 patient died of a probable catastrophic antiphospholipid syndrome. Patients with antiphospholipid syndrome, primary or secondary to systemic lupus erythematosus, may develop malignant hypertension with renal insufficiency and intrarenal vascular lesions, in the absence of lupus nephritis.