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Recent preliminary results from the PAMELA experiment indicate the presenceof an excess of cosmic ray positrons above 10 GeV. In this letter, we considerpossibility that this signal is the result of dark matter annihilations takingplace in the halo of the Milky Way. Rather than focusing on a specific particlephysics model, we take a phenomenological approach and consider a variety ofmasses and two-body annihilation modes, including W+W-, ZZ, b bbar, tau+ tau-,mu+ mu-, and e+e. We also consider a range of diffusion parameters consistentwith current cosmic ray data. We find that a significant upturn in the positronfraction above 10 GeV is compatible with a wide range of dark matterannihilation modes, although very large annihilation cross sections and/orboost factors arising from inhomogeneities in the local dark matterdistribution are required to produce the observed intensity of the signal. Wecomment on constraints from gamma rays, synchrotron emission, and cosmic rayantiproton measurements.

High Energy Positrons From Annihilating Dark Matter