Band-to-band Auger recombination is the dominant recombination mechanism in silicon at high carrier concentrations. Previous calculations found Auger rates too small to account for experiment. These calculations, however, contained uncontrolled approximations. We calculate accurate Auger recombination rates in both n-type and p-type silicon, avoiding approximations made in all prior Auger work. Our calculations show that Auger recombination is an order of magnitude stronger than previously thought. Our results for n-type Si agree well with experimental lifetimes. In contrast, a phonon-assisted mechanism is indicated for p-type Si. This conclusion can be understood based on details of the band structure. © 1990 The American Physical Society.