Recently, there has been increasing interest in whole-body photoacoustic tomography. Photoacoustic tomography utilizes non-ionizing laser illumination to generate a local temperature rise, which is subsequently converted to pressure via thermoelastic expansion. The pressure waves are detected by ultrasonic transducers, and the temporal signals are reconstructed to form an image of the optical absorbers. The hybrid nature enables photoacoustic tomography to generate high resolution images in both ballistic and diffusive regimes.6 In the past few years, several whole-body photoacoustic imaging systems, employing different light delivery and acoustic detection schemes, have been proposed.7–12 However, these systems either have limited detection views, such as half-ring and hemispherical, rendering inaccurate reconstruction of target boundaries,9,10,12,13 or require long scanning time, which increases motion artifacts.7,8 The use of fiber bundles also limits the efficiency and uniformity of light delivery. Ideally, a whole-body cross-sectional imaging system should employ uniform free-space ring-shaped light delivery and full-ring ultrasound detection. However, due to the technological difficulties in combining them non-obstructively with animal translation and acoustic coupling mechanisms, this approach has never been demonstrated in photoacoustic whole-body imaging. In this report, we present a ring-shaped confocal photoacoustic computed tomography system (RC-PACT) to overcome the aforementioned limitations and technological difficulties. RC-PACT utilizes free-space full-ring light delivery toward only the image cross section to provide high fluence illumination. The photoacoustic signals are detected by a cylindrically focused 512-element full-ring ultrasonic transducer array. The full-ring coverage enables RC-PACT to provide fast and accurate tomographic inversion of cross-sections with complete boundaries.