If My Dog Hasn't Defecated In A Week Although Urinates Regularly And Otherwise Acts Normal, Should I Be Concerned?

If he has not it is a serious problem.  Do not wait, right now, get him to the vet!  I nearly lost my little dog a few months ago.  She had swallowed a pecan from a neighbor's tree whole and couldn't pass it.  She too was urinating, but I could tell she was uncomfortable as she could not lie still for more than a couple of minutes.  She just looked uncomfortable.  She had defacated 3 days prior and the emergency vet was still ready to do surgery for even that is too long.  She had also become severely dehydrated but we had no idea of that.  X-rays are needed, although palpation in the office will be first.  Please do not wait.  As soon as you read this you must take action.

You need to get him to the vet as soon as you can. Not going to the bathroom for such a long period of time can cause him to pass away. It can literally kill him! Hope this helps, good luck. Go now!

Yes you should certainly be concerned, it's possible that he has an intestinal blockage that's preventing him from going. This is very dangerous. It could also be that he's just constipated, but he definitely needs checking out.

Theme,

It is a problem if your dog has not defecated in a week.  If that is the case see your veterinarian to confirm via x-ray that your dog is constipated and to assess the severity of the constipation.  Some dogs like their privacy when "using the bathroom" so make sure the dog is not sneaking off somewhere and defecating without your knowledge. 
Fiber is something we use in dogs to encourage defecation by bulking the diet to help move things through.  Canned pumpkin (non-spiced), dose dependent upon size is a great source of fiber.  Good Luck!

Ann Falk, DVM