The Crank-Nicolson (CN) version of the finite-difference time-domain (FDTD) method is applied to the analysis of multiconductor transmission lines (MTLs). Stability and dispersion issues are investigated for different cases, including single and multiconductor lossless and lossy lines. It is shown that for MTLs, the stability of the CN-FDTD method is conditioned by the structure of coupling matrices. Sufficient conditions for unconditional stability are derived. Four practical problems are analyzed using the CN-FDTD method. Numerical results are compared to measurements and leap-frog method. For the first three cases, using the CN method, the Courant number can be increased by a factor of 50 with good agreement with measurement results.