Previous computations of ion trajectories in the monopole mass spectrometer [P. H. Dawson and N. P. Whetten, Rev. Sci. Instr. 39, 1417 (1968)], for ion injection parallel to the instrument axis, have predicted asymmetric peaks with a tail on the low mass side and only 40% ion transmission. This is because an off-axis object cannot be completely focused at the exit from the analyzer. It is shown here that superior focusing at the analyzer exit, leading to symmetrical peaks, 100% ion transmission and, in some conditions, a reduction in the necessary rod-Vee Block spacing, and therefore in rf power, can be obtained by proper use of a fringing field at the monopole entrance. A simple linear entrance ramp, where ion trajectories are mathematically unstable, and which is apparently harmful to the quadrupole mass filter [W. M. Brubaker, Advan. Mass Spectry. 4, 293 (1967)], can be beneficial in the monopole. Examples of computed ion trajectories and peak shapes are given and various entrance ramps are compared. The chance use of an entrance ramp probably explains some of the high performance monopoles that have been constructed.