Method for the assembly of the structure of an aircraft which comprises defining on a chassis at least first and second templates (A, B) such that both are opposite and parallel to one another, where said templates (A, B) in turn comprise a plurality of through holes (a, b) such that each of the through holes of the first template corresponds to a complementary through hole in the second template; and where once said templates have been defined, the method comprises the following steps: 1. taking an initial measurement of the chassis and the templates (A, B) to identify the relative positions with respect to one another and to know their real position in space, obtaining the coordinates of points (a r, b r) of the through holes (a, b) forming the "real axis;" 2. placing laser equipment on two complementary through holes of said templates (A, B) for taking coaxiality and distance measurements of the laser beam of a collimator obtaining the real "x" and "z" coordinates of the points (a L, b L), which are the points through which the laser beam passes; 3. performing the calculation of the mathematical equation H of the straight line of the laser beam of the collimator passing through (a L, b L), and thereby obtaining the path of the laser beam, and therefore of the target points of the elements to be assembled; 4. performing the mathematical calculation of the coordinates x L c and z L c of the target point where the laser beam must strike when the element is positioned in its theoretical position; 5. performing the calculation of the target readings Δ x S c and Δ z S c which a coaxiality sensor has to show and Δy c T which a rangefinder has to show when the laser beam is in the target point calculated in the previous step 4, and therefore the positioned element such that the installer can readily and directly read in the apparatus if the element is well-positioned; 6. positioning the element until the values read by the coaxiality sensor and the rangefinder coincide with those calculated in the previous step 5; 7. fixing the element to the structure to be assembled by means of a definitive fixing type; 8. repeating the preceding steps 2 to 7 for each element until the assembly of the structure has been completed. 1. taking an initial measurement of the chassis and the templates (A, B) to identify the relative positions with respect to one another and to know their real position in space, obtaining the coordinates of points (a r, b r) of the through holes (a, b) forming the "real axis;" 2. placing laser equipment on two complementary through holes of said templates (A, B) for taking coaxiality and distance measurements of the laser beam of a collimator obtaining the real "x" and "z" coordinates of the points (a L, b L), which are the points through which the laser beam passes; 3. performing the calculation of the mathematical equation H of the straight line of the laser beam of the collimator passing through (a L, b L), and thereby obtaining the path of the laser beam, and therefore of the target points of the elements to be assembled; 4. performing the mathematical calculation of the coordinates x L c and z L c of the target point where the laser beam must strike when the element is positioned in its theoretical position; 5. performing the calculation of the target readings Δ x S c and Δ z S c which a coaxiality sensor has to show and Δy c T which a rangefinder has to show when the laser beam is in the target point calculated in the previous step 4, and therefore the positioned element such that the installer can readily and directly read in the apparatus if the element is well-positioned; 6. positioning the element until the values read by the coaxiality sensor and the rangefinder coincide with those calculated in the previous step 5; 7. fixing the element to the structure to be assembled by means of a definitive fixing type; 8. repeating the preceding steps 2 to 7 for each element until the assembly of the structure has been completed.