Protective helmet comprising: - a crown provided with a frontal part, an occipital part and first and second lateral parts each separating the frontal part and the occipital part, - a head support fixed to the crown to form a U shape, the head support comprising a frontal part and first and second lateral parts separated by the frontal part, - a first attachment point fixing a first end of the head support to the first lateral part of the crown, - a second attachment point fixing a second end of the head support to the second lateral part of the crown, - means for adjusting the head support configured to increase or reduce the length of the head support between the first and second attachment points, the means for adjusting the head support are located at the interface between the frontal part and each of the first and second lateral parts of the head support, the means for adjusting the head support being fixed to the crown by means of the frontal part and the first and second lateral parts of the head support, the means for adjusting the head support being arranged between an attachment point of the frontal part of the head support and each of the first and second attachment points of the first and second lateral parts of the head support - a neckband fitted in movable manner so as to move towards or away from the frontal part of the head support, the protective helmet being characterised in that; the neckband has two additional attachment points with the crown, the two additional attachment points being arranged in fixed manner on the crown independently from the length of the head support, - and in that the protective helmet comprises means for adjusting the position of the neckband configured to define the position of the neckband with respect to the frontal part of the head support, the means for adjusting the position of the neckband being distinct from the means for adjusting the head support to adjust the position of the neckband and the length of the head support independently from one another, and - the attachment point by which the frontal part of the head support is fixed to the frontal part of the crown is deformable so that an increase of the length of the head support corresponds to movement of the frontal part of the head support and the frontal part of the crown towards one another and a reduction of the length of the head support corresponds to movement of the frontal part of the head support and the frontal part of the crown away from one another, the frontal part of the head support being fitted movable with respect to the first and second attachment points. - a crown provided with a frontal part, an occipital part and first and second lateral parts each separating the frontal part and the occipital part, - a head support fixed to the crown to form a U shape, the head support comprising a frontal part and first and second lateral parts separated by the frontal part, - a first attachment point fixing a first end of the head support to the first lateral part of the crown, - a second attachment point fixing a second end of the head support to the second lateral part of the crown, - means for adjusting the head support configured to increase or reduce the length of the head support between the first and second attachment points, the means for adjusting the head support are located at the interface between the frontal part and each of the first and second lateral parts of the head support, the means for adjusting the head support being fixed to the crown by means of the frontal part and the first and second lateral parts of the head support, the means for adjusting the head support being arranged between an attachment point of the frontal part of the head support and each of the first and second attachment points of the first and second lateral parts of the head support - a neckband fitted in movable manner so as to move towards or away from the frontal part of the head support, the protective helmet being characterised in that; the neckband has two additional attachment points with the crown, the two additional attachment points being arranged in fixed manner on the crown independently from the length of the head support, - and in that the protective helmet comprises means for adjusting the position of the neckband configured to define the position of the neckband with respect to the frontal part of the head support, the means for adjusting the position of the neckband being distinct from the means for adjusting the head support to adjust the position of the neckband and the length of the head support independently from one another, and - the attachment point by which the frontal part of the head support is fixed to the frontal part of the crown is deformable so that an increase of the length of the head support corresponds to movement of the frontal part of the head support and the frontal part of the crown towards one another and a reduction of the length of the head support corresponds to movement of the frontal part of the head support and the frontal part of the crown away from one another, the frontal part of the head support being fitted movable with respect to the first and second attachment points.