This paper presents the results of geomorphological research of the periglacial relief on mountain Crnook (1881 m) in Southeast Serbia. The results have showed the significant presence of modern periglacial morphology on this mountain which is developing in azonal conditions of a periglacial mountain environment. Research results from Crnook are significant because they represent the continuation of similar studies on medium-high mountains of Serbia (Kopaonik, Stara Planina). Based on a comparison of data from Kopaonik, Stara Planina and Crnook (Nešić D., Milinčić M., 2004; Belij S. et al., 2008; Nešić D. et al., 2009; Nešić D., 2009), it can be concluded that in similar climatic frameworks with a significant share of anthropogenic activities, in terms of reducing the forest area in the highest parts of a mountain, similar modern periglacial processes develop on mountains as an indicator of azonal or boundary development framework of modern mountain periglacial environment. During 2006-07, the project "Modern periglacial geomorphic landforms on the mountains of Serbia" was initiated and the field research was conducted on the high mountains of Serbia (Stara Planina, Kopaonik, Kučaj, Beljanica, Zlatibor), and the mountains of Southeast Serbia (Vardenik, Besna Kobila, Dukat i Crnook).