A new ansatz for quark and lepton mass matrices is proposed in the context of supersymmetric grand unified theories. The 13 parameters describing fermion masses and mixings are determined in terms of only 6 free parameters, allowing 7 testable predictions. The values of V(us), V(cb), V(ub), m(u) m(d), m(s), and m(b) are then predicted as a function of the 3 charged lepton masses, m(c), m(t) and tan beta, the ratio of Higgs vacuum expectation values. In particular the Cabibbo angle and m(s)/m(d) are determined in terms of only lepton masses. All predictions are in very good agreement with experiments.