The richest Americans' share of national income has hit a postwar record, surpassing the highs reached in the 1990s bull market, and underlining the divergence of economic fortunes blamed for fueling anxiety among American workers.

The wealthiest 1% of Americans earned 21.2% of all income in 2005, according to new data from the Internal Revenue Service. That is up sharply from 19% in 2004, and surpasses the previous high of 20.8% set in 2000, at the peak of the previous bull market in stocks.

The...