Neurological deficits were found at the level of the lumbar spinal cord and roots in a patient with acromegaly. Myelographic and surgical examination revealed this to be due to compression by thickened ligamentum flavum. Although ligamentum flavum hypertrophy is not uncommon, it is usually seen in trauma as a result of tearing and scar formation or in spondylosis. This is the first case report of such a condition due to acromegaly in which the neurological symptoms are more often due to peripheral nerve and muscle abnormalities. Pathological examination of the excised ligamentum flavum revealed normal elastic tissue as compared to several surgical and postmortem specimens. Relief of neurological deficits followed excision of the hypertrophic ligamentum flavum.