Samui: Dr Somsak, across from the Chaweng post office on the ring road. 077-230-600.
Absolutely fantastic, excellent skills and assessment, and very compassionate bedside manner. If he cannot fix the problem, he tells you. Keeps up to date on latest treatments and local diseases. Very kind with strays. Extremely clean clinic. Treats emergencies on arrival. No nonsense, but extremely kind. He knew every one of my family by name and took care of the many injured strays I brought in, often for no charge. Used him since he arrived (geez, forget when!) We even smuggled animals into Chaweng hospital for xrays. I think his new office has those facilities now. Also another animal hospital further south along the ring road that does blood tests, etc. But, I have a soft spot for Somsak and his staff. Like family. My file there is as thick as "War and Peace".
Dunno about surgery on Samui. Friends took their injured dog to a Phuket hospital.
As SBK said, PAC on Koh Phangnan is great. Is the Irish vet in Hong Kong still volunteering there?
And, in my view, the real vets in Thailand (not the ones who just administer steroids to fighting cocks) are as good as any I've seen in Canada, where the prices are 20 times higher. One of my dogs was poisoned in pre-Somsak days, so rang my sis in Canada. She called her vet and he had no idea what to do. Thank the gods for the Internet.