An adjustable auto-clasp barrette includes a base, a hinged and clasped locking arm, and a resilient leaf spring positioned between the base and the locking arm. The locking arm and the leaf spring cooperate to engage the hair to secure the barrette in the user's hair. An adjustment coupling permits the positions of the leaf spring ends to be longitudinally adjusted relative to the base to increase or decrease how much the leaf spring deflects and bows outwardly. With the spring ends positioned farther apart the leaf spring is less bowed for holding thicker hair or a larger volume of finer hair. And with the spring ends positioned closer together the leaf spring is more bowed for holding finer hair or a smaller volume of thick hair.