The present disclosure provides shortening prevention sleeves for adjustable underground utility boxes, underground utility boxes including such sleeves, and methods of preventing shortening of underground utility boxes with such sleeves. A sleeve comprises a substantially rigid elongate tube that defines an internal cavity. The tube is configured to allow a stem portion of an adjustable underground utility box to extend fully therethrough via the internal cavity. The sleeve also comprises an opening that extends along the length of the tube and provides a passageway into the internal cavity. The tube is configured to allow the stem portion of the box to pass through the opening and into the internal cavity. The sleeve is configured to extend over and along the stem portion and between enlarged top and bottom portions of the box to prevent the stem portion, and thereby the box as a whole, from shortening.