found this on National Mental health association website... its a bit old 1991but it had some numbers and so on where you can get more information about the disorder.

http://www.nmha.org/infoctr/factsheets/26.cfm

Dysthymia

What is Dysthymia?
Dysthymia (the Greek roots of the word mean “bad state of mind” or “ill humor”) is a disorder with similar but longer-lasting and milder symptoms than clinical depression. By the standard psychiatric definition, this disorder lasts for at least two years, but is less disabling than major depression; for example, victims are usually able to go on working and do not need to be hospitalized.

How Common Is It?
About three percent of the population will suffer from dysthymia at some time - a rate slightly lower than the rate of major depression. Like major depression, dysthymia occurs twice as often in women as it does in men. It is also more common among the poor and the unmarried. The symptoms usually appear in adolescence or young adulthood but in some cases do not emerge until middle age.

Warning Signs
The warning signs of dysthymia are:

poor school/work performance
social withdrawal
shyness
irritable hostility
conflicts with family and friends
physiological abnormalities
sleep irregularities
parents with major depression
At least three-quarters of people with dysthymia have some other psychiatric or medical disorder as well.

Current Treatments for Dysthymia
Therapy:

Psychotherapy or cognitive therapy (also known as “talk therapy”) is used to alter people ’s self-defeating thoughts.
Behavioral therapy may help people learn how to act in a more “positive approach” to life and to communicate better with friends, family, and co-workers.
Medications:
Tricyclic antidepressants, the standard treatment for major depression, may be useful for dysthymia

In many cases, the symptoms are hard to recognize and classify, and the response to treatment is unpredictable. Most people with dysthymia see only their family doctor, who may misdiagnose them, especially if the main complaints are physical. Many people do not think of themselves as depressed, and are relieved to be told they have a treatable illness. Unfortunately, mental health professionals are usually consulted only when major depression develops, although dysthymia alone may lead to alcoholism or suicide. Even when it is recognized, dysthymia is difficult to treat. The longer a depression lasts the slower the recovery.

For More Information:
Contact your local Mental Health Association, community mental health center, or:
National Mental Health Association
2000 N. Beauregard Street, 6th Floor
Alexandria, VA 22311
Phone 703/684-7722
Fax 703/684-5968
Mental Health Resource Center 800/969-NMHA
TTY Line 800/433-5959

National Foundation for Depressive Illness (NFDI)
PO Box 2257
New York, NY 10016
Phone: (800) 248-4344

Depression Awareness, Recognition, and Treatment (DART)
National Institute of Mental Health
5600 Fishers Lane, Room 10-85
Rockville, MD 20857-8030
Phone: (800) 421-4211

American Psychiatric Association
1400 K Street, NW
Suite 501
Washington, DC 20005
Phone: (202) 682-6000

Source: The Harvard Mental Health Letter, May 1991 issue