Posterior mitral valve (MV) leaflet aneurysms are extremely rare complications of infective endocarditis (IE). When MV aneurysms occur, they usually involve the anterior leaflet. Real time three-dimensional transesophageal echocardiography (RT3D TEE) has been recently developed and provides views of unparalleled quality by optimizing visualization of spatial relationships. We present a rare case of a posterior MV leaflet aneurysm due to IE in a 64-year-old woman, best visualized by RT3D TEE.