Functional assessment of patients with osteosarcoma may yield unique insights into the guide and advance treatment. A range of patient-reported outcomes has been validated, including general health and condition-specific measures as well as computer adaptive testing. Health state utility measures, which facilitate comparative-effectiveness research, are also available. Beyond these surveys, and laboratory-dependent gait analyses, is the potential for real-world evaluation through research-oriented and consumer-oriented accelerometers. Initial studies have shown promising validity of these activity trackers and may also have implications for traditional oncologic outcomes.