Unilateral cortical necrosis is a rare condition, and only described in a few case reports. We present a case of a previously healthy 24-year-old male with acute unilateral cortical necrosis, where contrast-enhanced ultrasound (CEUS) became a valuable diagnostic tool. Antiphospholipid syndrome was subsequently diagnosed. Primary antiphospholipid syndrome is a well-known, but rare cause of cortical necrosis. It promotes thrombosis in renal arteries, capillaries and veins, and usually affects both kidneys. Unilateral cortical necrosis due to antiphospholipid syndrome has, to our knowledge, not been previously described.