Chronic adrenal insufficiency is an endocrine disease caused by insufficient secretion of adrenal hormones due to dysfunction of one or more links of the hypothalamic-pituitary-adrenal axis. The highest prevalence has been documented in Scandinavian countries: 15–22 people per 100,000 population, while other European countries report 10 cases per 100,000 population. Autoimmune adrenalitis is the most common cause of primary adrenal insufficiency in adults, and it can be either alone (40 %) or a component of autoimmune polyglandular syndromes (60 %). The etiologic factors of primary adrenal insufficiency include tuberculosis or AIDS. These causes of adrenal cortical insufficiency are particularly relevant in Ukraine. The article describes a clinical case of a patient with both primary adrenal insufficiency and Werlhof’s disease. The prevalence of adrenal insufficiency and etiologic factors of primary adrenal insufficiency are highlighted. A detailed differential diagnosis of primary adrenal insufficiency with other diseases that could cause clinical symptoms such as hypoglycemic states, severe weight loss, hypotension, severe muscle weakness, hyponatremia, hyperkalemia is performed. The basic principles of diagnosis, treatment, and prognosis in primary adrenal insufficiency are discussed. Despite typical, specific manifestations of adrenal insufficiency, diagnosis in real clinical practice is difficult. Awareness and vigilance of doctors regarding the symptoms of adrenal insufficiency is necessary. Late detection of chronic adrenal insufficiency can lead to complications. Timely diagnosis and treatment of chronic adrenal insufficiency improves disease prognosis and quality of life.