A method for the time-domain simulation of multiconductor transmission lines with frequency-dependent conductor (skin effect) and dielectric losses is presented. The method is based on a traveling-wave solution of the transmission line equations in the frequency domain, which reduces to the conventional modal solution for lossless lines when no losses are present. Time-domain simulation for the lossy care is achieved by convolving the transmission line terminal voltage with describing time-domain input and transfer impulse responses for the multiconductor line. Careful formulation of the frequency-dependent conductor and dielectric losses assures causality in the transmission line responses. The numerical burden of discrete-time convolution is avoided by approximating the transmission line responses with exponential series. An implementation of the solution algorithm in SPICE is described. Examples are included for coupled lossy stripline and microstrip configurations.>