The form is due yearly on the extended due date of your US. Income tax return. It is filed with your personal return and includes information on the foreign corporation's ownership, formation, income and expenses, and assets and liabilities. Usually it will not result in any additional tax due with your personal return, but that is possible if it has Subpart F income.
In most situations (unless the flow through election is made as explained below) the form 5471 does not result in any additional tax on your US tax return. However, if the foreign corporation has a sufficient amount of investment income, income from the sole owners personal services, or income from reselling goods made by an affiliate in the US, its income may become immediately taxable to you the shareholder. Subpart F income is complex which means a careful analysis of the sources of the corporations income must be made to determine if it is immediately taxable to its shareholder. If another owner of the foreign corporation files the form, you just need to identify data on that owner in an attachment to your tax return.
If the corporation owns real estate, and possible for other reasons, it is advisable that it is formed a a Sociedad de Responsibilidad Limitada (SRL). You as the owner of the SRL can make an election for US income tax purposes to treat it as a flow through entity on the US return of its owner. (This is the same as the treatment of an LLC or partnership for US tax purposes.) This means all of its income or losses flow through to you on your personal tax return and becomes a part of your US taxable income each year. It also allows you to take a foreign tax credit on your personal return for any taxes the foreign corporation pays in Mexico on its income. This election also stops any possibility of double taxation or converting capitals gains into ordinary income on your US income tax return.
If the IRS discovers you filed late or you should have been filing this form and did not the penalty is $10,000 per year for each unfiled form. There is a tax treaty between Mexico and the U.S which allows both countries access to the other countries records. Your US passport is included with other documents in the bureau where your Mexican corporation is is registered in Mexico.
We recommend to you that you file this form each year if you have the requisite stock ownership in a Mexican Corporation. Failure to file could result in extreme IRS penalties if they discovered you failed to file.