Flatback deformity is the complication of lumbar and lumbosacral fusions characterized by loss of lumbar lordosis with a resultant forward inclination of the trunk. This can lead to difficulty standing erect, and patients commonly endorse pain in the knees and anterior thighs from maintaining a flexed knee posture to position their trunk upright. They also endorse early fatigue, a subjective sense of imbalance, and difficulty with horizontal gaze. Treatment of flatback deformity requires operative intervention, and surgery often involves three-column osteotomies given the rigid nature of the deformity. Though originally described in the context of degenerative pathologies, flatback deformity can also occur following vertebral column tumor resection, often because the prioritization of oncologic cure during the index operation can divert attention from the need to prevent or correct the associated deformity. Increasingly, it is acknowledged that comprehensive treatment of vertebral column tumors requires assessment of baseline deformity, and the surgical plan must seek to correct existing deformity while at the same time avoid the generation of iatrogenic deformity. This is especially important given the improved prognoses of patients with spine tumors. In this chapter, we describe the evaluation and management of flatback deformity in the setting of vertebral column tumor resection.