Abstract: An adjustable protective helmet having a substantially rigid outer bowl-shaped shell sized larger that the user's head, and having inner padding inside of the shell sized to fit on the user's head but with a looser fit than desired. The adjustment structure includes a flexible strap extended through circumferentially spaced slots in the shell to extend both inside of and outside of the shell, to its ends outside of the shell sized to overlap one another. A rivet secures the underlying strap end to the shell. The padding between the shell slots is free from connection with the shell, and the strap in this region overlies the padding between the padding and shell and is secured to the padding. Quick release fastening pads on the overlapping strap ends allow them to be releasibly secured together. The strap can thus be tightened via the overlying strap end from outside of the shell and connected to the underlying strap end to establish the helmet fit desired.