Conn's syndrome is a disease of the adrenal glands involving excess production of a hormone, called aldosterone. Another name for the condition is primary hyperaldosteronism.

Conn's syndrome is important because it is a potentially curable cause of high blood pressure (hypertension). Some studies suggest that Conn's syndrome is rare (one new case in a million people each year). However, when detailed investigations have been performed in patients with high blood pressure, up to 15 per cent may have this condition.

High blood pressure (hypertension) is the main, and often the only, symptom.

Other symptoms may occur because high aldosterone levels in the blood act on the kidney to increase the loss of the mineral potassium in the urine. This in turn may lead to a fall in blood potassium, resulting in tiredness, muscle weakness and passing of large volumes of urine (polyuria), especially at night (nocturia). However, these symptoms are also found in many other conditions (for example, diabetes mellitus or hypercalcaemia) and do not, by themselves, establish a diagnosis of Conn's syndrome. Also, many patients with proven Conn's syndrome do not have a low blood potassium level.