ETF assets grew $56.6 billion or 12% to $534 billion in December according to a report published by State Street Global Advisors.

The largest growth was in International ETFs, up $14 billion or 16% and Size/Market-Cap ETFs, up $26 billion or 17%. Sector ETFs declined $1.4 billion or 3%.

The 12% growth for ETFs compares well to all asset classes which experienced smaller increases for the month.  U.S. equities (S&P 500) were up 1.1%, international equities (EAFE) were up 6.0%, U.S. treasuries were up 3.4% and bonds were up 3.7%.

State Street continued to gain share in December, up 4 points to 30%.  For all of 2008, State Street saw $70 billion of net inflows into the SPDR ETF family.