The method of moments with full domain polynomial expansion is used to calculate the characteristic impedance of a dielectric microstrip transmission line with the edge condition taken into account. The values calculated by this method are in good agreement with the results reported by Farrar and Adams (see Engineering Index 1970 p 2851, abstract 28951). The principle advantages of the present method are that the computation time is substantially reduced and the charge distribution on the dielectric sheet can be determined accurately.