BACKGROUND: Simultaneous bilateral total hip arthroplasty (SimBTHA) is often performed in younger, fitter patients with bilateral hip disease. If patients are deemed not suitable for SimBTHA due to concurrent comorbidity, it may be more appropriate to perform staged bilateral total hip arthroplasties (StBTHAs) 3-6 months apart to minimize complications and morbidity. Complication rates following hip arthroplasty are low and large national datasets are helpful for assessing these rare events. We aimed at comparing SimBTHA vs StBTHA in order to determine any differences in morbidity and mortality. METHODS: Hospital Episode Statistics data for all patients who underwent bilateral THAs in the English National Health Service between April 2005 and July 2014 were obtained. Patients were grouped into SimBTHAs (same day) or staged, with the second THA occurring between 3 and 6 months after the first. Medical and surgical complications were compared and total length of stay was assessed. RESULTS: A total of 2507 underwent SimBTHAs and 9915 had StBTHAs. SimBTHA patients were significantly younger (60.6 vs 65.5 years, P < .001) and more likely to be male, but had similar Charlson comorbidity scores. Compared to StBTHAs, patients undergoing SimBTHAs had a greater risk of pulmonary embolism, myocardial infarction, renal failure, chest infection, and inhospital death. Patients undergoing SimBTHAs had a significantly shorter overall hospital stay (8.9 vs 10.4 days). Patients undergoing SimBTHA at high-volume units had a lower average Charlson score and subsequent complication rate than low-volume units. CONCLUSION: These findings highlight the greater risks of SimBTHA in patients with Charlson score greater than 0 performed at lower-volume centers in England.