Conventional CT and MRI scans provide exquisite anatomic detail of soft tissue sarcomas but fall short of estimating the degree of tumor viability within a sarcomatous mass. Functional imaging methods that measure biologic properties within sarcomas may be better able to determine true tumor responses to chemotherapy or radiotherapy. Many different approaches to measure biologic processes have been taken and are discussed, but positron emission tomography (PET) is currently the most quantitative and developed. A response in tumor glucose uptake, determined by PET, has been shown to correlate with improved clinical outcomes in high-grade extremity soft tissue sarcomas and gastrointestinal stromal tumors. Functional imaging of soft tissue sarcomas may prove to be useful clinically, therefore further investigation is warranted.