Are mosquitoes repelled by high frequency sound?
After seeing your question, I decided to do a bit of research on the topic.



First Source: EurekAlert!


http://www.eurekalert.org/pub_releases/2007-04/jws-mrt041607.php


  "Mosquito repellents that emit high-pitched sounds don't prevent
  bites"


Some key-points from the webpage:


  A Cochrane Systematic Review of the use of electronic mosquito repellents (EMRs) failed to find any evidence that they work. 
  
  To test these claims a team of Cochrane Researchers conducted a systematic review looking for trials conducted with EMRs. They located ten field trials that had been carried out in various parts of the world. None of these trials showed any evidence that EMRs work.
  
  All ten studies found that there was no difference in the number of mosquitoes found on the bare body parts of the human participants with or without an EMR




Second Source: Wikipedia


http://en.wikipedia.org/wiki/Insect_repellent


  These electronic devices have been shown to have no effect as a mosquito repellent by studies done by the EPA and many universities.




Third Source: CBCnews


http://www.cbc.ca/news/story/2007/04/18/mosquito-repellent.html
Key points from the article:


  "There was no evidence in the field studies to support any repelling effects of EMRs, hence >no evidence to support their promotion or use"
             
  -Ahmadali Enayati, researcher


This is a major point as well:


  The study also said that in 12 of the 15 experiments, the landing rates of mosquitoes on subjects was in fact higher than in control groups.


The article also points out that female mosquitoes can't hear very well- Which supports the idea that high-frequency repellents are ineffective; Much more than you probably think. Why? Well, it's pretty simple:

Female Mosquitoes are the only Gender that Bite.



Overall, when you consider the countless studies and research put in to the effects of high-frequency sounds on mosquitoes, it's pretty obvious that:
No.High Frequency Sounds do NOT repel mosquitoes