The numerical technique of discrete light-cone quantization (DLCQ) is applied to a single-fermion truncation of Yukawa theory in four dimensions. The truncated theory is regulated by three Pauli-Villars bosons, which are introduced directly in the DLCQ Fock-state basis. A special form of the Lanczos diagonalization algorithm is used to handle the indefinite metric. Renormalization is done nonperturbatively.