An adjustably expandable suture anchor is provided. The suture anchor includes a pair of members, one of which includes a suture mount, which are configured to be secured together in a selected one of a plurality of positions to cause one of the members to expand by an amount that corresponds to the selected position. In one embodiment, the expandable member is an outer member, and the other member is an inner member which is progressively insertable into an opening in a body of the outer member and securable in the selected position therein. For example, the inner member is threaded into the outer member body or is inserted into the body in ratchet-like fashion. As the inner member is inserted distally into the outer member, an exterior enlargement on the inner member engages a plurality of arms which extend proximally from body, and causes the arms to progressively expand radially outwardly. Because the amount of expansion is adjustable, the suture anchor can be customized to provide the proper amount of fixation for the quality of the bone in which the anchor is installed. For example, when used in relatively soft bone tissue, the suture anchor can be expanded to a greater degree than might be required in harder bone tissue to obtain secure fixation.