They come once a year and they check for mold and mildew in the crawlspace. The service has been good! They make sure there are no leaks and nothing coming in through the plastic. The only problem I had was that the dehumidifier was not working. They got on it right away and they fixed it. We got a new dehumidifier and they also installed a new sump pump and drainage tile. Our house is a lot better and it was worth is to us because the basement smelled like it was damp. I have been very pleased with them. The service was worth it because there was a lot of mildew. The also had to scrub down the crawlspace twice and there has been a vast improvement. We would definitely hire them again!