Polycythemia may not cause any symptoms. It's often discovered only if a hemoglobin test or a red blood cell count is done. Some people do experience symptoms that appear gradually. These may include itching following bathing, dizziness, and a flushing of the face and hands. Weakness, headaches, visual disturbances, and a sense of "fullness" in the head and in the left upper abdomen may also be associated with the condition. Some people may have high blood pressure.

An infant who has polycythemia may be feeding poorly and have low blood sugar and difficulty breathing. It's very important to note that the problem isn't a cause for major concern in babies. It often doesn't require treatment, and it often resolves within a few days. However, these symptoms do warrant a visit to the doctor. Only very rarely does polycythemia cause serious problems in babies, such as seizures due to poor circulation to the brain.

Anyone who has polycythemia vera must receive treatment. Without treatment, the symptoms will become much worse and the risk of death from stroke, blood clots, or heart attack will increase. With proper treatment, the average survival of people with polycythemia vera is 7 to 15 years. People will probably feel quite normal and their risk of stroke or heart attack will be much less than if they didn't seek treatment. Although there's no cure, most people live for more than 10 years with the disease. Blood clots are the most common cause of death, followed by complications of myeloid metaplasia (a progressive disease of the bone marrow), hemorrhage, and development of acute leukemia.