Anaesthesia-related complications and mortality have been significantly reduced in the last years.(1) Nevertheless, anaesthesia-related side effects, such as post-operative delirium and sleep disturbances should not be underestimated. These side effects are economically challenging because they may lead to prolonged hospital stay and change in lifestyle condition. (2) After general anesthesia' sleep disturbances frequently occur. They are featured by insomnia' hyperinsomnia' narcolepsy' and changed sleep structure. (3.4) There are a lot of risk factors associated with post-operative sleep disturbance such as patient age, preoperative comorbidity, severity of surgical trauma, postoperative pain, postoperative complications and presence of pre-operative fatigue and depression. (5) Insomnia is one of the most prevalent health problems during pre-operative period and after post-operative recovery. It can lead to increase incidence of post-operative complications such as delayed recovery , anxiety and delirium (6). Post-operative delirium is also one of the most common complications following anaesthesia with frequency estimates ranging from 10 to 50%. It is defined as delirium occurring 24 to 72 hours after surgery. (7) There are multiple risk factors for developing postoperative delirium including pre-existing dementia, old age, medical co-morbidities, and psycopathological symptoms. The recognition and treatment of Post-operative delirium is critically important because postoperative delirium is associated with poor outcomes including functional decline, dementia, cognitive impairment, increased hospital length of stay , increased mortality ( 11% increasing in the risk of death at 3 months and up to a 17% increased risk of death at 1 year. (8) Animal studies have found that Magnesium can regulate melatonin production which is a hormone that guide body sleep wake cycle (9) . Magnesium is an essential cofactor for many enzymatic reactions' especially those that are involved in energy metabolism and neurotransmitter synthesis. It is a cofactor involved in more than 300 enzyme systems' regulates diverse biochemical reactions in the body (10.11) . Magnesium supplements were used to improve insomnia symptom among older people in a double blinded placebo controlled clinical trial(12). Low dietary Magnesium intake was found to be significantly associated with depression which is a potential risk factor for insomnia(13). Also using Magnesium sulphate as an adjuvant has been associated with significantly less analgesic requirements and reducing postoperative pain which can improve quality of sleep and decrease insomnia symptoms.(14) AIM OF THE STUDY The aim of this work is to identify the potential predictors of postoperative delirium and insomnia in patients undergoing lumbar fixation under general anesthesia, and to evaluate the effect of intraoperative administration of Magnesium sulphate on the occurrence of post-operative delirium and insomnia in those patients.