A single owner of a U.S. LLC is by default a disregarded entity for U.S. federal income tax purposes. Essentially, this means the entity is transparent for U.S. tax purposes. A single owner may file an election, under certain circumstances, to be treated as an S corporation or a C corporation. A foreign owned U.S. disregarded entity must file Form 5472 each year to report the business activity of the LLC, as well as information about the non-resident owner. The owner completes this task by filing a proforma Form 1120 with the Form 5472 attached. It's very important that these returns are filed timely and accurately. The IRS has recently increased the penalty for noncompliance from $10,000 to $25,000.