Indoor parasitic cellular systems are in-building stand alone cellular networks that use the concept of simultaneously reusing the frequencies of cellular systems outside the building for wireless communications inside the building. The objective of this thesis is to provide an analysis to determine the frequency reuse possible between in-building and outside cellular systems. The amount of frequency reuse currently available for an urban office building is presented based on field strength measurements made inside the building. In addition, this thesis describes the simulation code written which models a growing cellular system for the purpose of analyzing the effect that a growing cellular system will have on in-building frequency reuse. Future in-building frequency reuse is predicted in three month intervals for a time period of six years based on the results of the simulation code.