If you filed your tax returns electronically, you can contact the IRS 72 hours after they've acknowledged receipt of your return.http://www.irs.gov/individuals/article/0,,id=96596,00.html If you have mailed your tax returns, the IRS suggests waiting three to four weeks after the postdate before checking your refund status.http://www.irs.gov/individuals/article/0,,id=96596,00.html 

To check your status online, go to the IRS website and click on "Where's My Refund?" The service will let you know whether or not your return has been processed, and when your refund was mailed out or deposited into your bank account. If there has been a delay, the site will provide you steps to initiate a refund trace.

You can also contact the IRS by phone at (800) 829-1040. You will be guided through an automated system where you'll enter the proper information to retrieve the data on your tax refund.https://sa1.www4.irs.gov/irfof/lang/en/irfofonlinehelp.jsp 

When you check your status online or by phone, here's what you'll need:

1. Social Security Number (or Individual Taxpayer Identification Number)http://www.irs.gov/individuals/article/0,,id=96596,00.html
2. Filing Status (Single, Married Filing Joint Return, Married Filing Separate Return, Head of Household, or Qualifying Widow(er)http://www.irs.gov/individuals/article/0,,id=96596,00.html
3. Exact whole dollar amount of your refundhttp://www.irs.gov/individuals/article/0,,id=96596,00.html
   

If you believe you should have received your return--and the IRS confirms that your return has been sent--you can file for a lost or stolen check. However, there is a minimum 28-day waiting period from the time the IRS claims to have sent the return before you can file it as lost or stolen.