In order to retrieve a lost ITIN (that is Individual Taxpayer Identification Number), you will need to call the IRS ITIN Hotline at 1-800-908-9982. You can answer a series of questions to verify your identity and the IRS will provide you the number.
Keep in mind, if it has been several years since the number has been used, the IRS will deactivate the ITIN and require you to resubmit the Form W-7 and required documentation (original passport) to obtain a new ITIN.
