The structure of the extracellular domain of human CD69 has been determined by single-crystal X-ray diffraction. The structure refined to 1.37 A resolution provides further details of the overall structure and the asymmetric interface between the monomers in the native dimer. The protein was crystallized using di[poly(ethylene glycol)] adipate, which also served as a cryoprotectant. This is the first report of a crystal structure determined using crystals grown with this polymer.