The Americans with Disabilities Act (ADA) requires employers to keep any medical information or documentation provided by employees confidential and separate from their regular personnel files. Employers must also retain this information for only as long as it is needed for the purpose for which it was collected.
It is a best practice to retain any ADA-related documentation, such as a request for an accommodation or documentation supporting the need for an accommodation, for the duration of the employee's employment plus one year after the employment relationship ends, in case of any dispute or need for reference in future.
It's important to note that the ADA does not have specific record retention requirements. But most other employment related laws like OSHA, FMLA also have similar record retention period. It is a good idea to consult with an attorney or HR professional to determine an appropriate retention period and ensure compliance with all relevant laws.