Are lilies poisonous to cats?

Yes, extremely. Every part of true lilies and day lilies is toxic to cats: petals, leaves, stems, pollen, even the water in the vase. A cat can suffer kidney failure from licking a little pollen off their coat. "Pollen-free" lilies are not safe either.

Keep lilies out of any home with a cat. If you think your cat has touched or chewed one, go to a vet immediately.

The long version: The first week with a kitten

General guidance, not a substitute for your vet. If your cat seems unwell, call them.