Abstract: A size adjustable cap utilizing a new and improved size adjustment strap is disclosed. The size adjustable cap has an opening in the back of the cap between the cap and the size adjustment strap which extends across the opening. The size adjustment strap has one end secured to the cap in the vicinity of a sweatband that is internally attached to the cap proximate its lower margin. The size adjustment strap has a free end and extends through a complementary shaped slot provided in the cap in the vicinity of the sweatband on an opposite side of the cap opening to allow the size adjustment strap to pass through the complementary shaped slot for positionment between the sweatband and the cap. Cooperating adjustment fasteners are associated with the size adjustment strap and the sweatband for engagement with one another when the size adjustment strap is positioned between the sweatband and the cap. Preferably, the cooperating adjustable fasteners are loop and hook fasteners.