National Underwriter's annual listing of the top U.S. reinsurers looks a little unusual this year, with two names usually found near the head of the list disappearing from the rankings entirely.

The two reinsurers in question--General Reinsurance Corp. and American Re-Insurance--reported negative premiums in 2005 on a net basis, causing them to lose the fifth- and eighth-place positions they held, respectively, based on 2004 net premiums.

Traditionally, in July, NU has listed the top reinsurers using net written premiums from the prior year contained in the National Association of Insurance Commissioners Annual Statement database, available via National Underwriter Insurance Data Services.