The 2008 IUCN Red List assessment classified P. deckenii as Vulnerable (VU). Forests in its range are already highly fragmented, and continued habitat loss is the greatest threat to its survival. Forests are burned to provide pasture for livestock and cut for charcoal production. The animal itself is protected by a very strong taboo in much of its range, becoming very tame as a result, but if the taboo were to break down for whatever reason the species could disappear very rapidly.
Decken’s sifaka occurs in three national parks (Baie de Baly, Tsingy de Bemaraha, and Tsingy de Namoroka), the Tsingy de Bemaraha Strict Nature Reserve, four special reserves (Ambohijanahary, Bemarivo, Kasijy, and Maningoza), and in at least one classified forest (Tsiombikibo) (Nicoll and Langrand, 1989; Hawkins et al., 1998; Garbutt, 2007; Thalmann et al., 1999, 2002; Randrianasoa et al., 2000; J. Durbin, pers. comm.; E. E. Louis Jr., pers. obs.).
As of 2010, this species was not being kept in captivity (I. J. Porton, pers. comm.).