Publisher Summary This chapter describes the diagnosis of pain in back. Pain in the back is one of the commonest complaints in general and specialist practice, and no specialism is immune from it. The differential diagnosis, therefore, covers most of medicine. The first important subdivision is into acute and chronic back pain. Acute pain in the back may occur in any febrile disorder, even after an injection of T.A.B. vaccine. A good example is dengue or break-bone fever. Such pains usually rapidly settle either when the cause is removed or as the injured tissues heal. Spondylolisthesis, usually in the lower lumbar spine, occurs as a result of a bilateral lesion in the pars interarticularis, that is, that bony bridge taht unites the superior articular facet and pedicle to the lamina and inferior articular process. A forward or backward retrospondylolisthesis displacement may also occur as a result of degeneration of an intervertebral disk resulting in instability of the upper vertebra and narrowing of the intervertebral foramina. Well-centered X-rays taken in full flexion and extension will show the lesion.