Premature ovarian failure was originally termed "premature menopause." The term more accurately reflects what is happening within the body. Essentially, if ovarian function ceases before age 40, it's considered POF. Here's a very informative news segment from October 2008 that serves as a great overview of POF
POF affects about 1-4% of women before age 40, or about 250,000-1 million women nationally.
Women are generally born with enough eggs in their ovaries so that they ovulate one each month from puberty until about the age of 50. At that time, the supply of eggs is used up and menopause occurs. But, in girls and young women with POF, something has happened to the supply of eggs in the ovaries at a young age. It could be a loss of eggs, a dysfunction of the eggs or the removal of the ovaries at a young age. Unlike menopause, this is not a natural occurrence. This loss of ovarian function is occurring at too young an age to be considered a natural, although premature, menopause. Premature Ovarian Failure usually occurs in women under the age of 40 and can happen as early as the teen years.
Many times, the cause of POF is never determined, but can be traced to genetics, autoimmune disorders, or surgical intervention.
About 6-8% of women with POF will conceive naturally, however, many build families using egg donors/IVF or adoption.
Currently, there is no known way to induce the ovaries to begin ovulating naturally again.
POF carries increased risks of osteoporosis and heart disease because of the decreases in the reproductive hormones that protect women during their childbearing years. HRT (hormone replacement therapy) is the recommended treatment for women with POF.
For a very detailed document about POF, I highly recommend reading found here as a PDF . It is quite comprehensive and is a good starting document to really undestand the complexities of POF.