Although almost all THA and TKA patients both inside and outside the USA received prophylaxis, a large proportion did not receive treatment in accordance with the ACCP guidelines. Our study may have overestimated the use of recommended prophylaxis as some participating investigators may have had a specific interest in VTE prophylaxis. Furthermore, although analyses were restricted to approximately three-quarters of patients who had outpatient follow-up data, their characteristics were similar to those in the entire population.