Many disturbances in the normal function of endoplasmic reticulum (ER) cause accumulation of unfolded proteins in the lumen of ER, triggering an evolutionary conserved response, termed the unfolded protein response (UPR). The UPR is the mechanism enabling cells to cope with unfolded proteins, accumulated in ER lumen after the cell has been exposed to various unfavorable conditions. The UPR process has strong prosurvival implications, but switches towards apoptotic cell death when the stress becomes severe and unsolvable. The hallmark of the cytoprotective branch of UPR is stimulation of the expression of ER chaperones, of which ORP150 has gained a great deal of attention. ORP150 has been identified as being overexpressed in the pathology of many diseases and is involved in the cellular response to environmental stress. Although some fragmentary results concerning ORP150 molecular activity have been presented, its exact mode of action still remains unclear. In this paper we focused on the role of ORP150 in the pathogenesis of the main types of ER stress-related diseases: diabetes, neurodegenerative diseases, cardiovascular diseases and cancer.