Symptoms of PNH vary from patient to patient, but common symptoms can be categorized as follows:
From a low red cell count (anemia) and/or the break-up of red cells (hemolysis): feeling extremely tired or weak (fatigue); shortness of breath; irregular heartbeat; rapid pulse; dizziness especially when standing up; headaches; coldness in your hands or feet; pale skin (pallor); chest pain; decreased alertness; weight loss; low appetite; and a shortened attention span.

From a low platelet count (thrombocytopenia): bruising; bleeding; and pinpoint red bleeding spots on the skin (petechiae).

From hemolysis and the resulting release of hemoglobin into the circulating blood: dark urine (caused by hemoglobinuria, meaning hemoglobin in the urine); fatigue; jaundice (yellowed skin or eyes) or gallstones from high levels of bilirubin; and blood clots in a vein (thrombosis). Most PNH patients do not exhibit hemolysis at the time of diagnosis but when hemolysis occurs blood clots are the most life-threatening aspect of PNH. Even though the name "paroxysmal nocturnal hemoglobinuria" refers to the sudden and irregular night-time accumulation of hemoglobin in urine, not all PNH patients have dark urine.

From blood clots and the spasms they can produce: pain in the abdomen, back, head, or esophagus (throat area); trouble swallowing (dysphagia); restless leg syndrome (RLS); and impotence in men.

The combinations of symptoms can interact. Anemia can exacerbate problems from blood clots. A low white cell count (neutropenia) and hemoglobinuria can both result in increased susceptibility to infections. In turn, flu, colds, infections, and other illnesses that activate the immune system may trigger increased hemolysis. Infections and hemoglobinuria can both contribute to kidney failure.

A rapid increase in hemolysis and the resulting symptoms of fatigue, pain, and/or dark urine is called a hemolytic crisis and requires consultation with your doctor, who may prescribe bed rest and hydration or hospitalization. Because some of these symptoms can result from other conditions, a patient who experiences one or more symptoms of PNH does not necessarily have PNH. For the same reason, PNH may not be recognized or diagnosed at first. It is essential to consult a doctor for a professional diagnosis. Low white blood cell counts and/or low platelet counts are not normally symptoms of PNH and may result from another bone marrow failure disease.