Since its appearance in Brasil, in 1990, the mobile phones showed a remarkably fast expansion, exceeding the number of fixed phones in 2003 and reaching 54 million of active subscribers in the middle of 2004. This dissertation analyses the process of diffusion of mobile telephony in Brasil and its objectives are (a) to understand how this process happened and (b) to find economic, technology or business decisions that may have influenced it. The diffusion process is based in epidemic theory of diffusion of innovations and this study analyses and discusses the most popular models of diffusion of innovations found in the literature. The data is analyzed by nonlinear and linear regression and the results of the research show that the process of diffusion of mobile phones in Brazil can be fitted in an epidemic innovation diffusion model which indicates that the growth is close to its inflexion point, where it began to slow down towards maturity. Finally, the research shows that competition, marketing expenses, tariffs and innovation were the factors that accelerated the speed of the diffusion of mobile telephony in Brasil.