Ultrasonography is a vital component of modern clinical care, with handheld probes routinely used for a variety of applications. However, handheld ultrasound imaging is limited by factors such as the partial-body field of view, operator dependency, contact-induced distortion, and lack of transmission contrast. Here, we demonstrate a new system enabling whole-body ultrasound tomography of humans in reflection and transmission modes. To generate 2D isotropically resolved images across the entire cross-section in vivo, we use a custom 512-element circular ultrasound receiver array with a rotating ultrasonic transmitter. We demonstrate this technique in regions such as the abdomen and legs in healthy volunteers. We also showcase two potential clinical extensions. First, we readily observe subcutaneous and preperitoneal abdominal adipose distributions in our images, enabling adipose thickness assessment over the body without ionizing radiation or mechanical deformation. Second, we demonstrate an approach for rapid (seven frame-per-second) biopsy needle localization with respect to internal tissue features. These capabilities make whole-body ultrasound tomography a potential practical tool for clinical needs currently unmet by other modalities.