Antiphospholipid syndrome can occur at any age and is more common in young and middle-aged people, more often in women than in men. Patients with other autoimmune diseases are more likely to develop antiphospholipid syndrome, especially in SLE. Approximately 10% of patients with lupus have APS in combination, and more than half of patients with APS have other autoimmune diseases. The presence of antiphospholipid antibodies in some patients without any clinical signs does not mean that they have APS, and the presence of both antiphospholipid antibodies and clinical signs associated with antiphospholipid syndrome is necessary to confirm the diagnosis of APS. However, patients who are positive for antiphospholipid antibodies are at risk for developing APS. Other risk factors for thrombosis include smoking, prolonged bed rest, pregnancy and puerperium, oral contraceptives and hormone replacement therapy, malignancy, and chronic renal insufficiency.