Inthis paper, two dimensional transmission line circuits are used to determine cutoff wavenumbers of homogeneous arbitrarily shaped cylindrical waveguides. The derived circuits depend mainly on long transmission line (LTL) circuits. The resonance frequencies of these circuits are the required cutoff frequencies of the guide. The problem is reduced to a simple eigenvalue problem, which is solved to get the required solution. Numerical results are given to compare results with available analytical solutions and results given by other reported methods.