The IRS is closing the net on U.S. overseas citizens who do not declare their foreign bank accounts. Global Tax Network, a mobility tax provider, has published this very helpful synopsis of the annual FBAR filing requirements. I'd suggest a click and read for anyone with overseas U.S. assignees.
US persons with financial accounts maintained outside the US must report these accounts to the US Department of the Treasury annually (on or before June 30) if the balance exceeds a certain level during the year. The accounts are reported annually on Financial Crimes Enforcement Network (FinCEN) Form 114, Report of Foreign Bank and Financial Accounts (FBAR). Due to continuing media attention of efforts to improve compliance in this area, individuals are becoming more aware of the filing requirements.