Antiphospholipid syndrome (APS) is a disorder characterized by antiphospholipid antibody positivity, arterial or venous thrombosis, and fetal loss. In APS, renal as well as vascular and glomerular involvement is observed. Systemic lupus erythematosus and other connective tissue diseases should be excluded to diagnose primary APS. Immunoglobulin M (IgM) nephropathy is characterized by single or dominant IgM deposition in glomerular mesangium. It often presents with hematuria and proteinuria. In a 45-year-old female patient admitted to our clinic with diabetes mellitus and proteinuria, fundus examination did not reveal diabetic retinopathy but a high anticardiolipin IgM and venous thrombosis in the upper extremity were observed. Renal biopsy revealed IgM nephropathy. The patient was diagnosed with primary APS and IgM nephropathy. Cyclophosphamide and steroid treatment was started. Her proteinuria decreased as a result of the treatment. Although, it is reported in the literature that primary APS coexists with other glomerulonephritis, we did not detect coexistence of primary APS and IgM nephropathy.