Restless legs syndrome (RLS) is a disorder of the part of the nervous system that causes an urge to move the legs. Because it usually interferes with sleep, it also is considered a sleep disorder.
People with restless legs syndrome have uncomfortable sensations in their legs (and sometimes arms or other parts of the body) and an irresistible urge to move their legs to relieve the sensations. The condition causes an uncomfortable, "itchy," "pins and needles," or "creepy crawly" feeling in the legs. The sensations are usually worse at rest, especially when lying or sitting.
The severity of RLS symptoms ranges from mild to intolerable. Symptoms can come and go and severity can also vary. The symptoms are generally worse in the evening and at night. For some people, symptoms may cause severe nightly sleep disruption that can significantly impair their quality of life.
Restless legs syndrome may affect up to 10% of the U.S. population. It affects both sexes, but is more common in women and may begin at any age, even in young children. Most people who are affected severely are middle-aged or older.
Source: Restless Legs Syndrome
Helpful link: Restless Legs Syndrome Foundation