In a protective helmet, especially a bicycle helmet, having a head band made of plastic, which is fastened to the helmet calotte and which is height adjustable for adapting to the head anatomy of the wearer, provision is made that the head band is supported on both sides of the helmet calotte so as to be pivotable and that extensions are provided that extend at both end regions of the head band approximately perpendicular to the same toward the top and interior of the helmet, which engage into holding elements that are fixed in the helmet calotte, the extensions being adjustable lengthwise relative to the holding elements.