Is it ethical for surgeons to operate on themselves? Possibly not, but I know of at least a dozen who've done their own vasectomies. OK, so it's hardly major surgery and with a Swiss Army knife, a supple back and a well-angled shaving mirror it should all be over in 10 minutes. But why bother when you could ask a mate to do it with half the hassle? Of the surgeons I've spoken to, the commonest reasons for turning a knife to your own scrotum are "to see if I can do it", "to make sure I get enough anaesthetic" and "so it's done properly". The last two hardly inspire confidence in the vasectomy industry, but as market forces have transformed snip clinics into conveyor belts, it's not unheard of for patients to be aware of what's happening down below and for surgeons to remove something other than a piece of vas deferens. One DIY surgeon was less concerned with his colleagues' competence as their confidentiality: "I didn't want another consultant to see my penis."

I'm sure they've got better things to laugh about in the reading room of the Royal College of Surgeons, but most doctors have a phobia about being examined intimately by other doctors. Men have been known to examine their own prostates rather than risk a colleague's gloved finger, and nearly every pregnant doctor I know has examined her own cervix. This is more out of curiosity than fear, to assess its ripeness. A normal cervix is firm and long, like a carrot. By the end of pregnancy, it goes short and mushy, like a warm marshmallow. A ripe cervix is ready for labour, and the inquisitive pregnant doctor may also give it a quick "sweep" to try to get things moving. This sounds desperate, but at 42 weeks with heartburn, piles and backache, you'll try anything.

Nurses too have been known to tamper with themselves. Last week, I met a sister who did her own cervical smears because of a bad experience with another nurse. It wasn't the cold speculum or the lack of jelly but her colleague's familiar manner that put her off. "It was like going to a Harvester's restaurant. She introduced herself as Julie, explained what everything on the trolley was and just as she was about to take the smear, she leant across, sniffed and said: "Ooh, that's a nice perfume." I've never been able to wear Rive Gauche since." In a way, doing your own smear isn't much different to examining your breasts, and if you've got the expertise, why not?

Less clear is whether health professionals should treat themselves or their families when they actually get sick. The General Medical Council takes a dim view of this, not least because it's hard to be rational when you are ill or someone you love is ill, but I suspect the practice is widespread. Last year, I ran a communication course for GPs using simulated consultations. One of the scenarios was a depressed GP who'd finally sought help after trying to treat himself. In the discussion that followed, it transpired that all the GPs in one of the small groups had been, or were currently, self-medicating with Prozac.

Mental illness is a particular problem for doctors who, in the macho culture they've been brought up in, may feel that they should be immune to such frailty. A diagnosis of depression can spell disaster for your career prospects and many go for months denying the problem and masking symptoms behind their professionalism. If that fails, they raid the drug cabinet.

As for doctor's relatives, most will tell you they don't get better treatment. We aren't very good at spotting what's going on under our noses, and besides, I don't mind being a family doctor, but I don't want to be a doctor to my family. In the past, doctors were only too keen to experiment on their kith and kin. Gerhard Domaghk, a pioneer of sulphonamide antibiotics, tried them out on his daughter first, and Edward Jenner inoculated his son with cowpox liquid to test his vaccination theories. Both got away with it and to this day doctors can be found jabbing their children or giving them antibiotics for snotty noses when they would tell their patients to make do with Calpol. We should seek another opinion, but doctors also hate treating other doctors. When you ask for help, the answer is usually: "What do you think we should do?"

Not that I ask for help very often. The last time I was in a GP's surgery was 16 years ago as a student with tonsillitis. The doctor looked in my mouth and then stuck his hands down the front of my pants. "What are you studying?" he asked. "Medicine," I replied. He flushed, removed his hands, mentioned something about checking for lymph glands and got me out of the door as quickly as possible. I've been treating myself ever since.