Background: One of the main issues regarding the management of chronic diseases is patients' non-adherence to treatment regimens. An important factor affecting treatment adherence is social support. This qualitative study was aimed at exploring the role of perceived social support in adherence to treatment regimens among patients with chronic diseases. Methods: A qualitative study was carried out on 34 patients with chronic diseases, who were purposively recruited from the targeted cities of Bushehr and Tehran, Iran. In-depth non-structured interviews were conducted for the process of data collection from June 2014 to November 2015. Data were constantly and simultaneously analyzed as they were being collected, using the content analysis approach. Results: The data collected in this study yielded four themes that included: having the wholehearted support of a spouse, living with supportive family members and significant others, obtaining information, and confiding in physicians. These themes showed the dimensions and the types of patients' perceived social support. Conclusions: The study's findings imply that the most important and common sources of perceived social support among Iranian patients with chronic illness are their spouses, relatives, and friends. According to the results, the participants realized that social support could help them in adhering to their treatments and coping with their illness. Identifying types of perceived social support allows health professionals, especially nurses, to use such information for developing and implementing evidence-based care plans and organizing support systems in order to enhance patients' adherence to treatments.