If you find incorrect information on your report, file a written dispute with the credit reporting bureau and the entity that listed the information. The credit reporting bureaus are required to investigate your dispute, usually within 30 days, unless your dispute is frivolous. After the investigation is done, the credit reporting bureau must give you the written results. If an inaccuracy was corrected, they also must give you a free copy of your report.
If the dispute isn't resolved in your favor, you can ask that a statement be included in your file and in future credit reports.
In addition to your free report every 12 months, you're entitled to a free report if any company takes the kind of adverse action against you that would wind up being reported to credit reporting bureaus, such as denying you credit, insurance or employment. You'll need to request the free report within 60 days of that happening.
You also can get a free report once a year if you're unemployed and you plan to look for a job within 60 days, or if you're on welfare, or if you've been a victim of fraud.
(Source: FTC, Consumer Credit Counseling Service)