The present invention relates to a method for selectively reducing the amount of assistance data transmitted to an assisted GPS equipped mobile terminal by excluding the transmission of assistance data relating to one or more satellites that are potentially visible to the mobile station. In the preferred embodiment one or more criteria are used to identify which of the potentially visible satellite are the least likely to be used by the mobile terminal in determining its position, and assistance data relating to the least likely satellites to be used is excluded from the assistance data that is to be transmitted to the mobile terminal. A determination of an optimal number of satellites for which assistance data should be sent to the mobile terminal.