Measuring rectal temperature

Lay your child face down across your lap. Put a dab of petroleum jelly (sample brand name: Vaseline) on the end of the thermometer. Then, gently insert the thermometer into the child's anus until the silver tip is not visible. This should be about 1/4 to 1/2 inch (6 to 12 millimeters) inside the anus. Hold the thermometer in place. Most digital thermometers work in less than 1 minute.