This research is an investigation of the causes of call drops in a GSM network in Benin City, Nigeria. Call drop is inability of call to connect and go through the network successfully. For a drop call the subscriber does not enter into a queue for potential assignment. In this work, a drive test was conducted over a period of three months (March, April and May 2010) in cells around Benin City area. The drive test was conducted with the use of test mobile. A test mobile is a kit comprising mobile phone, drive testing proprietary software called TERMS on a laptop computer and GPS (global positioning system). A total of twenty seven cells out of forty cells around Benin City area were discovered to have severe call drops leading to very poor network performance. The problems that caused the call drops were determined and corrected leading to high improvement in call performance.