What does ACVIM stand for at the end of a vet's name?

ACVIM stands for "American College of Veterinary Internal Medicine". A veterinarian with this acronym behind his/her name has completed an additional three years of rigorous study specifically focusing on internal medicine (gastrointestinal, endocrine, etc.) and has passed an additional test to prove he/she has advanced knowledge relating to internal medicine. This veterinarian would be referred to as a board-certified specialist and will generally charge a higher fee for treating your pet.