A Method and arrangement for determining the position of mobile terminals in a cell of a mobile communication network where time alignment (TA) is employed for terminal transmissions in timeslots to a serving base station. First, the distance to the base station is determined (200) for at least one mobile terminal in the call using a TA independent positioning method. A current TA value used by the at least one mobile terminal for time alignment of signal transmissions in an allocated timeslot, is also obtained (202). A relation between the determined TA independent distance and the obtained current TA value for each mobile terminal, is then estimated (204), and a TA bias of the cell is determined (206) based on the estimated relation. The position of any subsequent terminals can then be determined using a TA based positioning method and the TA bias, such that the current TA value used by the subsequent terminal is adjusted by the TA bias. Thereby, the TA based positioning method will become more closely related to the true terminal position.