It could be, but a strong urine smell from a neutered cat (he IS neutered,
right??) can be a sign of concentrated urine. That would indicate that he
isn't getting enough water inside him, which can lead to problems with
bladder and kidney stones later in life.
You don't mention if he eats wet or dry food, but a lot of cats who eat
exclusively dry food don't get enough water, as cats often don't have a
strong thirst drive.
If the cat is an intact tom, well, their urine usually smells rather strong.
You still need to make sure they get enough water, though.
You don't mention the cat's age or physical state, either, so it could be the
result of a maturing male tom or illness.

IANAV: As always, when in doubt, call your vet.

Ruth,

Sound an infection.  I'm not a vet, but I would immediately call your vet,
ask to speak to him/her or a vet tech, and describe in detail his symtoms
and ask them what they would recommend. They may just let you come by their
office to pick it (antibiotic) up. Good luck to you and keep us posted.

ML