Background: The effect of early surgery in elderly patients with hip fractures has been controversial during the last five decades due to equivocal evidence both in favour and against it. The objective of this thesis is to systematically assess all the available evidence on the effect(s) of early surgery compared with delayed surgery in elderly patients with hip fractures. Methods: Searches for randomised controlled trials (RCTs) or prospective observational studies were conducted from inception to July 2017 in the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (OVID), EMBASE (OVID), and they were complemented with list of references searching, review of both clinical trials registers and archives of orthopaedic meetings. Two reviewers independently selected studies for inclusion, extracted data and evaluated risk of bias; and a third reviewer resolved discrepancies. Risk ratios (RR) were calculated for dichotomous data, and mean difference (MD) or standardised mean difference (SMD) was calculated for continuous data. The quality of evidence was assessed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach. Results: 39 studies were included with 51,857 participants (range of mean age: 74 to 93 years) comparing early versus delayed surgery. Three studies were RCTs and 36 were observational studies. The evidence from RCTs and observational studies showed that early surgery reduces risk of all-cause 3 mortality in elderly patients with a hip fracture (RR 0.73, 95% confidence interval (CI) 0.65 to 0.83; I2 = 67%; number needed to treat for benefit (NNTB) 20; low quality of evidence). Observational studies showed reduced risk of all-cause mortality by early surgery at 6 (RR 0.77, 95% CI 0.66 to 0.91; I2 = 56%; very low quality of evidence) and 12 months postoperative (RR 0.69, 95% CI 0.55 to 0.87; I2 = 76%; very low quality of evidence), and when surgery is performed within the first 48 hours upon hospital admission (RR 0.72, 95% CI 0.62 to 0.84; I2 = 65%; very low quality of evidence). Observational studies also showed a reduction of complications (RR 0.61, 95% CI 0.51 to 0.73; I2 = 64%; very low quality of evidence) and length of hospital stay (MD -5.06, 95% CI -6.52 to -3.60; I2 = 87%; very low quality of evidence) by early surgery, but the evidence was uncertain for functionality (SMD 0.05, 95% CI -0.04 to 0.14; I2 = 0%; low quality of evidence) and pain (RR 0.89, 95% CI 0.67 to 1.17; I2 = 0%; very low quality of evidence). RCTs showed that early surgery reduces length of stay (MD -6.73, 95% CI -12.92 to -0.54; I2 = 54%; very low quality of evidence) and improves functionality (SMD 0.32, 95% CI 0.04 to 0.59; I2 = 5%; low quality of evidence). Conclusions: Low-quality evidence showed that early surgery reduces all-cause mortality at 6 and 12 months post-surgery, especially when it is performed during the first 48 hours after hospital admission. There was very low-quality evidence of a reduction in complications including pneumonia and pressure sores, and low-quality evidence for a reduced risk of urinary tract infection for early compared with delayed surgery. Reductions in length of hospital stay and improvement of postoperative functionality with early surgery were also observed but with very low- and low-quality of evidence respectively. There was very low-quality evidence for no effect of early surgery on postoperative pain.