New bridgeless single phase ac-dc power factor correction (PFC) rectifiers based on Sepic and Cuk topologies are proposed. The absence of an input diode bridge and the presence of only two semiconductor switches in the current flowing path during each switching cycle results in less conduction losses and improved thermal management compared to the conventional Sepic and Cuk PFC converters. The proposed topologies are designed to work in discontinuous conduction mode (DCM) to achieve almost unity power factor in a simple and effective manner. The DCM operation gives additional advantages such as: zero-current turn-on in the power switches, zero-current turn-off in the output diode, and reduces the complexity of the control circuitry. The proposed rectifiers are investigated theoretically. Performance comparisons between the proposed and conventional Sepic PFC rectifiers are performed. Simulation and experimental results are provided for a design example of a 65W/48V at 100 Vrms line voltage to evaluate the performance of the proposed PFC rectifier.