The diagnosis of antiphospholipid syndrome (APS) relies on clinical and laboratory criteria, which have been recently outlined in specific consensus conferences. Renal involvement in APS is not infrequent and includes different clinical patterns. For clinical purposes a distinction can be made between large vessel and microvascular involvement. Renal artery stenosis is frequent in APS. In case of microvascular involvement with an acute clinical course a differential diagnosis with other thrombotic microangiopathic diseases has to be made, taking in account thrombotic thrombocytopenic purpura, hemolytic uremic syndrome, malignant hypertension, drug nephrotoxicity (cyclosporin) and others. The disease is often chronic, with hypertension, different degrees of renal insufficiency and mild proteinuria. In patients with systemic lupus erythematosus and antiphospholipid antibodies the prognosis of kidney disease is generally poorer than in lupus alone. Finally, the kidney is almost invariably a target in catastrophic antiphospholipid syndrome. Anticoagulation is the therapy of choice, especially in arterial stenosis and acute disease, but is probably also indicated in chronic and subacute patterns. The role of immunomodulatory therapy has to be assessed.