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The three-body decay ' 0~2p + 'OC was studied following production via single-neutron stripping from a radioactive "0 projectile. This is the first observation of two-proton emission from an unbound ground state where the one-proton emission channel is energetically closed beyond the lightest case of Be. No evidence for He emission is seen, despite predictions for a large diproton branching ratio. An upper limit of 7% (95% C.L. ) is established for this decay branch. The implications of the small diproton branching ratio observed here and seen previously in Be are discussed.PACS numbers: 2~.50.+z, 25.60.+v, 27.20.+n Over 30 years ago Goldanskii predicted the existence of ground-state two-proton (2p) radioactivity in particle unbound (proton-rich) even-Z nuclei where the pairing energy between the last two protons causes the one-proton