There are a couple of different treatments that could be - borate is often injected into wood that way, and there are several other termiticides that are placed directly into the wood by drilling holes.
Borate generally lasts for the entire life of the wood, but other products you inject don't last that long.
Liquid treatments (the kind designed to create a chemical barrier the termites can't cross) generally last for five years - but that's subject to correct application.
Sometimes, if a gap is left in the treatment the termites can find a way back in before that time period is up. There can be all kinds of factors that make it last more or less than that, such as the local environment, and it's hard to give a very precise answer.
Soil treatments (the same kind of thing, but applied to the soil) have a ton of variation - they can go away in a few days or they can last years.
Bait treatments (where you put stakes around your yard with a bait station for the termites to eat) will last as long as there's bait in the station.
In short, it's really tough to tell. Some products last for many years, but still don't keep termites out of your house if there's a "gap" in the treatment area. Application, the soil in your area, rain, and a ton of other factors can affect the answer. Your best bet is to ask for a guarantee from the exterminator that it will work for a certain period of time. Many companies will do this as a matter of course, and some states require it by law.
If you have a question about termites you want answered, submit it here.
Sources and Useful Links:
Return to Termites Guide Home Page
Text copyright 2007 Killthetermites.com and may not be reproduced without consent. This is not the official web page of any of the products listed on this site, this is a review page created by an individual.