A method of determining a geographic position of a user terminal comprising a receiver of signals of a global navigation satellite system, the method comprising having the user terminal: - performing pseudo-range measurements related to a plurality of signals received from transmitters of the global navigation satellite system, said plurality of signals received from transmitters of the global navigation satellite system comprising a number of received signals greater than the number of unknown variables, wherein the unknown variables are the geographic coordinates defining the geographic position of the user terminal to be determined and the clock offset between the user terminal clock and the global navigation satellite system clock; - calculating ( 315, 320) a first estimation of the geographic position of the user terminal based on the pseudo-range measurements by means of a weighted least square method; - calculating post-fit residuals for the first estimation of the geographic position; - comparing the calculated post-fit residuals to a first threshold, characterized in that the method further comprises the step of - in case the first threshold is exceeded, calculating a second estimation of the geographic position of the user terminal based on the first estimation of the geographic position and on the post-fit residuals using a Monte-Carlo method, otherwise retaining the first estimation of the geographic position as the geographic position of the mobile communications terminal, wherein said calculating a second estimation of the geographic position using the Monte-Carlo method comprises: - defining a width of a set of candidate solutions for the application of the Monte Carlo method, said width depending on information made available as a result of the calculation of the first estimation of the geographic position using the weighted least square method. - performing pseudo-range measurements related to a plurality of signals received from transmitters of the global navigation satellite system, said plurality of signals received from transmitters of the global navigation satellite system comprising a number of received signals greater than the number of unknown variables, wherein the unknown variables are the geographic coordinates defining the geographic position of the user terminal to be determined and the clock offset between the user terminal clock and the global navigation satellite system clock; - calculating ( 315, 320) a first estimation of the geographic position of the user terminal based on the pseudo-range measurements by means of a weighted least square method; - calculating post-fit residuals for the first estimation of the geographic position; - comparing the calculated post-fit residuals to a first threshold, characterized in that the method further comprises the step of - in case the first threshold is exceeded, calculating a second estimation of the geographic position of the user terminal based on the first estimation of the geographic position and on the post-fit residuals using a Monte-Carlo method, otherwise retaining the first estimation of the geographic position as the geographic position of the mobile communications terminal, - defining a width of a set of candidate solutions for the application of the Monte Carlo method, said width depending on information made available as a result of the calculation of the first estimation of the geographic position using the weighted least square method.