A method and arrangement in a terminal evaluation unit for detecting a malfunctioning terminal in a cellular network is provided. Connection data is received from at least one network node in the cellular network, wherein the connection data is referring to connections of terminals when present in cells of the cellular network. A mean connection drop rate is calculated based on the connection data for the terminals when present at least in a first cell during a preset time period. An individual connection drop rate which is associated with the first terminal is determined from the connection data. Deciding, based on a ratio between the individual connection drop rate and the mean drop rate, whether or not the first terminal is malfunctioning and providing the result from the deciding action to a cellular network operator for further evaluation.