Here are the ten worst-performing stocks in the S&P 500 index for 2010*.

Lumber, pulp and paper company Weyerhaeuser (NYSE: WY) was the worst performing stock in the index for the year, plunging more than 56 percent, largely due to the dismal conditions in the U.S. housing market.

The second worst performer, Dean Foods (NYSE: DF), down 52 percent, has suffered from rising commodity prices and consumers’ preference for cheaper groceries.

1. Weyerhaeuser (NYSE: WY)                                       -56.07%
2. Dean Foods (NYSE: DF)                                          -52.00%
3. H&R Block (NYSE: HRB)                                           -47.88%
4. Apollo Group (Nasdaq: APOL)                                 -34.47%
5. Diamond Offshore Drilling (NYSE: DO)                     -33.01%
6. PulteGroup Inc. (NYSE: PHM)                                   -25.60%
7. Micron Technology (NYSE: MU)                                -25.19%
8. Supervalu Inc. (NYSE: SVU)                                      -24.94%
9. AK Steel Holding (NYSE: AKS)                                 -24.54%
10. Western Digital (NYSE: WDC)                                  -23.78%

*Data from S&P (through yesterday's close)