The Social Security program responsible for disability assessment and payments is called Supplemental Security Income. SSI is designed to provide a minimum income to individuals who have been disabled and can no longer work. The amount of the monthly disability benefit you receive is determined by your average lifetime earnings. In 2010 the maximum individual SSI disability benefit is $674 a month with the maximum SSI benefit for an eligible couple set at $1011 monthly.
Contact the SSA by telephone or in person with your request. It is not possible to request a replacement check or a copy of a check using the automated website services.
Follow the instructions of the SSA representative. Depending on the circumstances, the SSA representative will either just ask you a few questions before putting your request into the system or in some cases ask you to fill out a form detailing the circumstances.
Wait for the SSA to respond to your request. The amount of time it takes to fulfill your request could range from a few days to a few weeks, so it is generally wise to follow up in person or by telephone after a week or so if it is an urgent matter.
Confirm that you really need a copy of your previous month's Social Security disability check. If it is for a lease, loan or another personal financial application, what you need is a "Proof of Income letter" and not an actual copy of your check. This can be requested online as part of the regular menu at the SSA website, and is a much less involved process than getting an actual copy of your check or a replacement check.