In the analysis of lightning surges, transmission towers are usually simulated by nonuniform lines, but overhead lines are assumed uniform. If the effect of line sags is considered, the variation of the overhead line parameters with respect to space should also be treated as nonuniform. Tower surge response is computed using nonuniform, single-phase line models for both transmission tower and ground wire. Using boundary conditions for these lines, total response of the system in s-domain is obtained. A fast inverse Laplace transform is used for the frequency-to-time domain conversion. The effect of line losses is included.