A bicycle saddle and handlebar height adjustment device including a tubular element provided with elements for its connection to the saddle, and presenting a portion cooperating with a support element for the tubular element. The support element is associated with a ring nut rotating thereon and presenting a first thread cooperating with a corresponding first counter-thread provided on the tubular element. An alignment element is present to maintain the angular position between the tubular element and the support element. The ring nut is associated with the support element by way of a second thread cooperating with a corresponding second counter-thread provided on the support element. The first and second threads are counter-rotating.