There is no short answer, really, when it comes to employee recordkeeping, thanks to numerous federal acts like Americans with Disabilities Act](http://www.ada.gov/), (http://www.dol.gov/whd/flsa/), and [Family Medical Leave Act, to name just a few.
As a general rule, you should keep records for the following years:
If you're involved in any employment-related dispute, especially with a terminated employee, you'll obviously want to keep all records until the dispute is settled.
You should also keep the medical and benefits records of employees who've been exposed to occupational hazards or diseases for 30 years.
States may also have requirements that you'll have to follow. For example, Missouri state law requires that you keep records for at least 3 years of:
You might want to search the internet for employee recordkeeping laws for specific requirements in your state.
The Society for Human Resource Management (SHRM) has a handy table that lists out exactly what records need to be saved based on the applicable federal law and how long each needs to be saved.
For requirements by state, visit SHRM here for recordkeeping laws.
Fact Sheet on Recordkeeping Requirements Under FLSA - DOL.gov - Department of Labor Sheet that details what records are to be kept by employers
Recordkeeping Requirements - EEOC.gov - US Equal Employment Opportunity Commission's Recordkeeping Requirements for employers
Access to Employee Exposure and Medical Records - OSHA.gov Occupational Safety and Health Administration's Requirements for access to medical records after exposure to hazardous substances