We have mapped CO and 2.6 mm continuum emission in the dwarf galaxy NGC 5253 with the Owens Valley Millimeter Array. CO is detected along the prominent dust lane in the nucleus. The CO emission is extremely weak: NGC 5253 appears to be the most CO-poor starburst known. The CO flux appears to be low by factors of ～100 compared to star-forming regions of similar radio and infrared luminosity in large spiral galaxies and as much as a factor of 10 weaker than those in other metal-poor dwarf galaxies. This unusually weak CO emission, together with the observed morphology of the CO gas and its unusual kinematical properties, lead us to suggest that NGC 5253 has recently accreted gas of extremely low metallicity, significantly lower than that of the galaxy itself.
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