Sports activity has many benefits in cancer survivors. A key one is having sport activity contribute to the well-being of the individual. However, there are no guidelines about the intensity and kind of postoperative mobility workouts after hip or knee megaprosthetic treatment. Opinion research about sports after modular bone and joint replacement may provide an understanding of surgeons’ attitudes on sports activity after megaprostheses of the hip and knee joint. A web survey with members of three international professional organizations of orthopedic tumor reconstructive surgeons was conducted between September 2016 and January 2018. Members were invited via personalized emails by the European Musculoskeletal Oncology Society (EMSOS), the International Society of Limb Salvage (ISOLS), and the Musculoskeletal Tumor Society (MSTS). The questionnaire included 26 questions. A total of 149 surgeons started the survey, and 76 finished the entire survey (American Association for Public Opinion Research (AAPOR) second response rate (RR2) EMSOS: 12.3%; ISOLS: 21.9%; MSTS: n/a). More than half of the respondents encourage sarcoma survivors after megaprosthetic treatment to reach an activity level that would allow them to regularly participate in active sporting events of University of California, Los Angeles (UCLA) activity level 7 and higher. Orthopedic tumor reconstructive surgeons do fear a number of complications (periprosthetic fracture, allograft failure/fracture, loosening, prosthetic or bearing failure, and early polyethylene wear) due to sports activity after modular bone–joint replacement, but they actually witness fewer complications than they conceptually anticipated. According to the surgeons’ opinions, between four to seven types of sports after surgery could reasonably be recommended depending on the type of hip or knee procedures. This survey provides insights into opinions on what could be recommended, what could be allowed if surgeons and their patients agree on the potential negative outcome, and which sports should definitely not be allowed after hip and knee megaprostheses.