Abstract: A sheet designed to cover a crib mattress, in a way in which a child will not be able to unravel the sheet, thereby creating a potential safety hazzard to the child. The present invention comprises a casement style sheet that completely covers the entire mattress. It slides onto the mattress through an opening in one end of the sheet. The perimeter of the opening having a continuous elastic band disposed therein, thereby allowing the sheet to fit tightly and tautly over the mattress without any snagging. The sheet is secured by a flap, which is integrally attached to the open end of the sheet, and is pulled over the encasement opening whereby it is then secured by hook and loop closure means.