We present results for the phase diagram of three-flavor QCDfor $mu_B < 500$ MeV.Our simulations are performed with an imaginary chemical potentialfor which the fermion determinant is positive. Physical observablesare then fitted by truncated Taylor series and continued toreal chemical potential. We map out the location of the criticalline $T_c(mu_B)$ with an accuracy up to terms of order $(mu_B/T)^6$.We also give first results on a determination of the critical endpointof the transition and its quark mass dependence.