A synchronous transmission (1) for a motorcycle comprises a primary shaft (51) of mechanical gearbox, and a pair of secondary shafts (52, 53) equipped with one or more secondary gearwheels for transmitting the motion to a hub shaft (75), wherein a desmodromic drum (70) actuates a pair of coupling forks (67, 68) selectively defining the position of respective sliding couplings (65, 66) between primary (51) and secondary shafts (52, 53) to select all speeds of the transmission, the desmodromic drum (70) being in phase with a device (80) for actuating the gearwheels, and wherein the coupling forks (67, 68) are equipped with a cam follower end (69) maneuvered by said desmodromic drum (70) having a cylindrical surface (79) whereon a single desmodromic track (19) is formed.