The market for IP telephony has increased over the years, more organizations integrate this technology with their existing networks. The advantages with IP telephony are the possibility to integrate different networks and transfer voice, data and video. However, the technology does not differ from other new technologies when it comes to handling security problems. The risks may increase when voice and data are transferred in the same network. Therefore it is important to elucidate the security aspects for IP networks. This thesis evaluates the technology by performing a comparison between traditional telephony and IP telephony in order to analyze the maintenance and security aspects of these two technologies. The comparison is based on the security services, authentication, integrity, confidentiality, non-repudiation and availability since these are the fundamental security aspects of IP telephony according to the authors. The result of the comparison indicates that IP telephony fulfils the most important security services, i.e. authentication, integrity and confidentiality. The PSTN (Public Switched Telephone Network) is seen as a secure network, because it is closed, e.g. only the operator has access.