how do i prune a very leggy rhododendrun?

Hi June welcome to GOY, you say that your Rhododendron is leggy, how old is it? is it newly planted and gone like this? is it old and just looks like seen better days? Has it flowered recently? Are there any other noticable problems with it? eg: leaf discolouration, curling leaves etc. Also do you have Acid soil, what aspect is it in? Sorry to bombard you with questions like this, but some more info would really help, as in general Rhododendrons don't really like hard pruning, the general advice is to purley remove damaged branches from there origin, and remove dead flower stems carefully as the new growth will appear directly below them. so i am trying to rule out any other problems that may be causing this. If it is just the case that it is very old, and needs a good hair cut to regenerate, then you can hard prune after it finishes flowering during spring. but i would avoid doing this unless all else fails.

In restored parkland at the bottom of my road are rhododendrons planted over 80 years ago. The parkland had become very overgrown and many of them had grown very tall, raching for the light. Since the park has been restored, many of the rhodos have started shooting from the base. So the answer is yes, they will regrow but if they have several stems, I would be inclined to spread the heavy cutting back over three years, doing about a third of the stems each year.
Some rhodos are also grafted on to root stock - you may still be able to see the graft low down. Make sure you DON'T cut below this point and also ensure any new shoots are coming from ABOVE it.