Purpose: This study aimed to identify the effect of spiritual well-being on the adaptation to chronic illness, among people with chronic illnesses. Design and Methods: The study comprised of 466 patients hospitalized in the internal medicine clinics of internal diseases, cardiology, neurology, and chest diseases, at the training and research hospital of a university. Findings: There was a significant positive relationship between spiritual well-being and adaptation and how spiritual well-being affected patients' adaptation to chronic illness. Practice Implication: Study results indicated that adaptation to chronic illness increased in direct relation to an increased level of spiritual well-being, among people with chronic illnesses. K E Y W O R D S adaptation, chronic illness, spiritual well-being 1 | INTRODUCTION Chronic illnesses progress slowly and are affected by physiopathological conditions; they cause irreversible changes, require lifelong follow-up and treatment, and are difficult to manage for both the patient and caregiver. 1,2 Untreated chronic illnesses are the primary causes of mortality and morbidity; their socioeconomic burden increases gradually, and they cause life-threatening complications, functional losses, repeated hospitalizations, and limitations in daily life activities. 3 Moreover, they affect numerous aspects of people's lives, including body image and lifestyle, dietary habits, and social relationships, and cause a variety of physical and mental symptoms, such as pain, anxiety, and stress. 1,4 In this sense, the effective management of chronic illnesses is crucial and, for it to be successful, it is important for people to know, accept, and adapt to all the changes that occur as a result of their chronic illnesses. Adaptation is a person's power to accept internal and external changes and exhibit suitable attitudes and behaviors. 5 It is a person's power to adhere to the treatment required, apply the recommended diet, accept the necessary lifestyle changes, and turn them into behaviors. 5,6 While the literature reviewed did not include any studies that evaluated adaptation to chronic illness using the Adaptation to Chronic Illness Scale (ACIS), studies evaluating adherence to drug therapy, 7 diet, and healthy lifestyle behaviors all reported problems in adherence. 8,9 These problems caused increased rates in mortality and repeated hospitalizations. 10,11 Consequently, ensuring adaptation to illness becomes vital for the effective management of illnesses. 12 According to the literature, understanding the illness and adapting to it in daily life is essential for the selfmanagement of chronic illnesses. 12,13 It was also reported that socioeconomic factors, cultural aspects, factors related to health teams and health services, and patient characteristics are also all contributing factors in a patient's ability to adapt to illness. 13,14 In this respect, it is crucial to evaluate the adaptation process with a holistic approach to care and in terms of physiological, psychological, social, an...