The incidence and severity of HZ (or shingles), as well as the frequency and severity of its complications, increases markedly with increasing age. More than half of all cases occur in persons over the age of 60. Even without complications, HZ can interfere with an elderly patient's ability to perform essential activities of daily living, resulting in a loss of independence that is emotionally devastating and frequently irreversible. The most common complication of HZ in elderly persons is postherpetic neuralgia (PHN), which frequently results in disordered sleep, chronic fatigue, anxiety and severe depression. Antiviral therapy has a modest impact on the acute phase of HZ. However, it does not appear to prevent the development of PHN.