The just-released Statistics of Income Bulletin (Summer 2004) includes Federal Estate Tax Returns Filed for Nonresident Aliens, 2001 and 2002, by Darien Berkowitz Jacobson (SOI). Here is the summary:

The number of nonresident alien decedents whose estates filed a regular Form 706NA was 139 in 2001 and 137 in 2002. The total gross estate in the U.S. of those that filed increased from $50.8 million in 2001 to $53.3 million in 2002.