Background. Prayer is commonly used among patients for health purposes. Therefore, this review focused on three main questions: (1) why do people turn to prayer in times of illness?, (2) what are the main topics of their prayers?, and (3) how do they pray? Method. We undertook a systematic review of the literature by searching the databases PubMed, Medline, and PsycINFO. The following inclusion criteria were used: (1) participants in the study were patients dealing with an illness, (2) the study examined the use of private rather than intercessory prayer, and (3) the content and purpose of prayer rather than its effects were investigated. Results. 16 articles were included in the final review. Participants suffered from a variety of chronic diseases, mostly cancer. Five main categories for the reasons and topics of prayer were found: (1) disease-centered prayer, (2) assurance-centered prayer, (3) God-centered prayer, (4) others-centered prayer, and (5) lamentations. Among these, disease-centered prayer was most common. Conclusions. Although most patients with chronic diseases do pray for relief from their physical and mental suffering, the intention of their prayers is not only for healing. Rather, prayer can be a resource that allows patients to positively transform the experience of their illness.