Photolytic degradation of decabromodiphenyl ether (BDE 209) has been observed in several matrices such as solvent/water mixtures, sediments, and soil; however, no studies have investigated the degradation potential of BDE 209 in house dust. In the present study, both a natural and a BDE 209–spiked dust material were exposed to sunlight for 200 cumulative h. Degradation of BDE 209 was observed in both matrices but was 35% greater in the spiked dust relative to the natural dust material. The pseudo-first-order degradation rates were 2.3 × 10−3 and 1.7 × 10−3 per hour for the spiked and natural dust, respectively. During the 200-h exposure, as much as 38% of the original BDE 209 mass was degraded in the spiked dust, 25% of which could not be accounted for and was lost to unknown pathways and/or products. The remaining 13% was accounted for by the formation of lower brominated congeners. Debrominated products detected in the spiked dust included all three nonabrominated congeners (BDE 206, BDE 207, and BDE 208) and several octabrominated congeners (BDE 196, BDE 197, BDE 201, BDE 202, and BDE 203/200). In technical commercial octa-BDE mixtures, BDE 201 is a very small component (below detection limit to 0.8%), and BDE 202 is not detected. Therefore, the presence of these congeners in house dust may provide a marker of environmental debromination of BDE 209. The ratio of BDE 197 to BDE 201 may also be indicative of BDE 209 degradation. as the ratio of these two congeners appeared to reach a steady-state value (∼1) in both exposure scenarios in the present study.