b {yields} s{gamma} and supersymmetry with large tan{beta}.

We discuss the constraints on the supersymmetric parameter space from the decay mode b {yields} s{gamma} for large values of tan{beta}. We improve the theoretical prediction for the decay rate by summing very large radiative corrections to all orders in perturbation theory. This extends the validity of the perturbative calculation to the large tan{beta} regime. This resummation of terms of order {alpha}{sub s}{sup n} tan{sup n+1}{beta} is based on a recently proposed effective Lagrangian for the Yukawa interaction of bottom quarks. Moreover, we identify an additional source of tan{beta}-enhanced terms, which are of order {alpha}{sub s} tan{beta} and involve the charged Higgs boson, and analyze their behavior in higher orders of perturbation theory. After correcting the current expressions for this rare decay branching ratio at next-to-leading order, we obtain that, contrary to recent claims, the measured branching ratio of b {yields} s{gamma} constrains the supersymmetric parameter space in a relevant way, even if tan{beta} is large.