The invention relates to an access control system and to a method for operating said system. The system uses a standard access control system (24, 8), which controls a plurality of access points (1) by means of respective individual physical closing mechanisms (8). According to the invention, at least one reader (2) and a controller (3), which is connected to the latter in order to control the closing mechanism (8), is provided at each access point (1) and the system is equipped with at least one access control server (4), which carries out the centralised management of access data and is connected to the respective controllers (3), in addition to at least one mobile telephone server (5), which is connected to the access control server (4), said mobile telephone server being at least indirectly capable of transmitting data to mobile radio telephone subscribers (7) via a mobile radio telephone network and of receiving data from said subscribers. The mobile radio telephone server (5) can also be an integral component of the access control server (4). The aim of the invention is to provide an access control system that uses mobile telephones, which can be easily retrofitted and is especially user-friendly and at the same time reliable. To achieve this, at least one access point (1) is equipped with a short-range transmitter (9), which transmits identification information that is specific to the access point in such a way that it is only received by a mobile telephone (7) located in the direct vicinity of the access point (1) and is used at least indirectly by said telephone to control the access verification process. The use of Bluetooth or WLAN transmitters (9) is particularly advantageous in this context as modern mobile telephones (7) are already equipped with interfaces of this type and Bluetooth transmitters (9) are cost-effective and readily available.