Illness experience can cause uncertainty in each stage of disease. Feelings of uncertainty also affect the emotions of patients. These emotions include anxiety, fear, anger, helplessness, hypersensitivity, grief and depression. Uncertainty makes it difficult for one to make decisions and decreases the level of control over one’s life. Investigation of this subject may be useful in the evaluation of patients by health professionals.  The literature on uncertainty in general medicine and illnesses was examined on Medline, and studies relevant to our experiences were selected and reviewed. Uncertainty is defined as a feeling of inadequacy based on not being able to control the situation. Uncertainty is a common experience for individuals living with disease, particularly when treatment cannot assure cure. When uncertainty is appraised as danger, emotion-focused coping strategies are expected to predominate since danger implies that the situation is unmanageable with the available self-control behaviors. In  the literature reviewed, uncertainty was found to be related to anxiety and coping. Successful adjustment is dependent on self-management and mastery. During an illness informing the patient decreases uncertainty; therefore, uncertainty is a subject which must be handled at each stage of the illness. While dealing with patients who experience uncertainty, the uncertainty during the diagnosis, treatment and rehabilitation should be thoroughly evaluated, in order to increase the patient’s quality of life. In addition, positive thinking, social support and financial security help one to cope with illness and prevent uncertainty. Although the importance of the subject is known, an insufficiency of direct studies on this subject has been noted in Turkey. There is a need for further studies on this subject.