Objective: Literature examining the effects of total hip arthroplasty (THA) on subsequent body weight gain is inconclusive. Determining the extent to which clinically relevant weight gain occurs following THA has important public health implications. Design: We used multi-variable logistic regression to compare data from one of the largest US-based THA registries to a population-based control sample from the same geographic region. We also identified factors that increased risk of clinically important weight gain specifically among persons undergoing THA. The outcome measure of interest was weight gain of ≥5% of body weight up to 5 years following surgery. Results: The multi-variable adjusted [age, sex, body mass index (BMI), education, comorbidity and pre-surgical weight change] odds ratio for important weight gain was 1.7 [95% confidence interval (CI), 1.06, 2.6] for a person with THA as compared to the control sample. Additional arthroplasty procedures during the 5-year follow-up further increased odds for important weight gain (OR = 2.0, 95% CI, 1.4, 2.7) relative to the control sample. A patient with THA had increased risk of important post-surgical weight gain of 12% (OR = 1.12, 95% CI, 1.08, 1.16) for every kilogram of pre-operative weight loss. Conclusions: While findings should be interpreted with caution because of missing follow-up weight data, patients with THA appear to be at increased risk of clinically important weight gain following surgery as compared to peers. Patients less than 60 years and who have lost a substantial amount of weight prior to surgery appear to be at particularly high risk of important post-surgical weight gain. © 2012 Osteoarthritis Research Society International.