Lumbar spine radiographs of 28 patients with Marfan syndrome and a gender and age-matched control group were evaluated for scoliosis and morphologic changes of the L2, L3, and L4 vertebrae. No patient or control subject had any serious low back problems. The Marfan patients showed a high incidence of scoliosis (64%). The incidence of lumbosacral transitional vertebra was also high (18%). The end plates of the vertebral bodies in the Marfan patients were more biconcave than in the control group. In addition, the transverse processes were longer in relation to the vertebral body width in the Marfan group than in the controls. These findings indicate that biconcave vertebral bodies can be added to the list of skeletal manifestations of the Marfan syndrome, and Marfan syndrome to the list of differential diagnoses for biconcave vertebrae ("codfish vertebrae").