An instrument case including a bottom wall, a top wall, and a primary side wall forming a first compartment. The primary side wall has a lower wall portion joined to the bottom wall and an upper wall portion joined to the top wall. Together, the upper and bottom walls have a substantially uniform width w to establish for the first compartment a first volume for accommodating an instrument having a maximum width no greater than the uniform width w. A flexible auxiliary side wall is contractible within the primary side wall and joins the bottom wall and the top wall. The auxiliary side wall has a substantially uniform width W greater than the width w of the primary side wall and is expandable to establish a second compartment with a second volume for accommodating an instrument having a maximum width greater than the uniform width w.