Just the one, for an inguinal hernia, 13 years ago. Way back in the 50's / 60's there was 'fashion' for having tonsils unnecessarily removed to stop you getting tonsillitis. This was probably before it was recognised that they have a role in the immune system.
I have a small scar on my chest which I thought was a birthmark. As a child I used to have a dream, more a feint recollection, of a nurse in her crisp blue uniform and a doctor looking at my chest. I was only and infant in my cot, so only weeks or months old. Many years later - I don't know how the subject came up - my mother said that when I was born, I had a cyst on my chest, and had a small 'operation' to remove it.
Generally, people will say that you don't have memory of things very early in your life, although one GP agreed that some early trauma can leave lasting memories.