Never leave your 401(k) with your previous company.

Whenever people switch a job, or retire from a company, they should take their 401(k) from their previous company and move it to a rollover IRA account with Vanguard, or Fidelity, or Charles Schwab.  The benefit is that you will have thousands mutual funds, stocks, bonds, and ETF's to choose from instead of 10 to 20 mutual funds' choises with the company's 401(k).  

If your situation is leaving a job, then you can roll over your 401(k).  Please read my two posts.

http://bbs.wenxuecity.com/tzlc/1175196.html

http://bbs.wenxuecity.com/tzlc/1175495.html

Good luck.