Background: Hospitalization of patients in an intensive care unit (ICU) is associated with a series of psychological problems for their family members called family intensive care unit syndrome (FICUS). Nonetheless, family members of patients in ICU often receive little attention from health care providers. Exploring family members' experiences of their patients' hospitalization in ICU helps health care providers focus more clearly on their problems.Aims and objectives: This study aimed to explore FICUS-related experiences among the family members of patients in ICU.Design: This was a qualitative content analysis study.Methods: This qualitative study was conducted in 2019. Participants were 14 family members of patients in ICU who were purposively selected from three hospitals in Tehran, Iran. Data were collected using semi-structured interviews and were analyzed using qualitative content analysis.Results: Participants' experiences of FICUS fell into four categories, that is, threat to psychological well-being (with four subcategories), threat to physical health (with three subcategories), threat to social health (with three subcategories), and change in spiritual orientation (with two subcategories).The 12 subcategories of these categories were emotional disturbances, hopelessness, changes in sleep pattern, mood changes, physical symptoms, aggravation of the existing illnesses, negligence towards personal health, alteration in social interactions, alteration in the burden of responsibility, alternation in the life process, resort to spiritual beliefs, and spiritual conflict, respectively.Conclusion: FICUS symptoms are not limited to psychological problems, rather they include a wide range of psychological, physical, social, and spiritual problems, which can affect the different aspects of family members' lives. Along with care delivery to patients in ICU, health care providers should provide care and support to patients' family members.