A cover adapted to be worn over a user's limb to shield a cast from water exposure includes a shell formed of a single layer of a flexible, water resistant and breathable material. The shell surrounds an interior of the cover, including a lower interior chamber and an upper interior chamber. An open top end communicates with the upper interior chamber and is sized to permit passage of the user's limb and the cast therethrough and into the upper and lower interior chambers. A cinch strap with a releasable securing mechanism closes the open top end around the user's limb. An inner cuff separating the interior chambers includes an elastomeric opening that fits snug against the user's limb, above the cast, and can be tightened using a secondary cinch strap and cooperating fasteners. A segment of water absorbing fabric on an interior surface for absorbing moisture and water.