The 2008 IUCN Red List assessment classified P. diadema as Endangered (EN). The principal threat to its survival is habitat loss due to slash-and-burn agriculture, logging, and mining. However, it is also severely affected by hunting in many parts of the range, even in existing protected areas (Green and Sussman, 1990; Mittermeier et al., 1992; Irwin and Ravelomanantsoa, 2004).
The diademed sifaka occurs in three national parks (Mananara-Nord, Mantadia, and Zahamena), two strict nature reserves (Betampona and Zahamena), three special reserves (Ambatovaky, Mangerivola, and Marotandrano) and in the recently-created Anjozorobe- Angavo Protected Area (Nicoll and Langrand, 1989; Britt et al., 1999; CBSG, 2002; Powzyk and Mowry, 2003). It has also been successfully reintroduced into the Analamazaotra Special Reserve at Andasibe; it once occurred naturally in this area but was extirpated 30–40 years ago. The reintroduction was carried out by E. E. Louis Jr. and a team of Malagasy researchers in 2007 with animals rescued from the nearby Ambatovy mine site.
Additional populations have been identified in two classified forests (Andriantantely and Tsinjoarivo), the Marokitay Forest Reserve, and in the unprotected
forests of Anosibe an’ala, Didy, Iofa, Maromiza and Sandranantitra (Lehman and Wright, 2000; Conservation International, 1999; Andriamasimanana et al., 2001; Andriaholirina et al., 2004; Garbutt, 2007). The Tsinjoarivo Classified Forest has been recommended as a new protected area, based on the presence of the unusual population of diademed sifakas found there.
As of 2010 only two individuals of this species were found in captivity, one in the Duke Lemur Center in Durham, North Carolina USA, and the other on Lemur Island, part of the Hotel Vakona in Andasibe, Madagascar (I. J. Porton, pers. comm.).