housetrained puppy had an accident?

First of all, clean it up thoroughly. Dogs develop a strong preference for using the same toilet area they've used before, so use an enzymatic cleanser to get rid of, not just cover up, the smell. Then, go back to the housetraining program and follow it to the letter. When your pup's had two accident-free weeks, you can slowly ease back out of housetraining.

Keep in mind that although puppies can grasp the concept of housetraining within a few weeks, they aren't physically capable of "holding it" for very long until they're six months of age at the earliest, and often closer to eight or nine months. Many people give their puppy free run of the house way too soon, inviting an accident. If your pup's younger than nine months, keep her in her crate or in a gated-off puppy playroom when you're not watching her closely, even if she seems housetrained.

What you shouldn't do is punish the dog for a mistake. It can actually create a housetraining problem, by making the pup afraid to eliminate in your presence.

If your puppy continues to have accidents, have her checked by a vet. Physical problems such as urinary tract infections can make it impossible for a puppy to hold it.