The diaper is disposable, being made of inexpensive waterproof plastic sheet material. The sheet is formed to a Z-fold, and stitched along its marginal edges. The pocket thus formed is open to the area beneath the dog's tail, for receiving solid excrement. A stitched-in absorbent pad extends forwards from the pocket, and receives liquid excrement. The action of assembling the diaper to the dog is effective to open the mouth of the pocket, and to press the diaper against the dog. The diaper is secured around the dog by means of Velcro tabs. Straps passing forward and around the dog's neck hold the diaper in place. The diaper includes a tail-hole, whereby the diaper is located in place on the dog.