A cast or bandage protector comprises a lightweight, plastic bag having a rectangular shape that is open at one end. The user can insert an arm or leg through the open end of the bag to protect a cast or bandage from getting wet. A strap encircles the bag adjacent the open end thereof. The strap is also made of plastic and has a buckle at one end that is free relative to the bag to allow access to be had to the underside of the buckle. The other free end of the strap can be threaded through the buckle and cinched back on itself to tighten the strap, and hence the open end of the bag, around the arm or leg of the user. The free end of the strap is secured in place by an adhesive patch that is pressed against the strap or bag. The protector is disposed of after a single use by stripping the protector off the arm or leg and throwing it away.