Difficulty finding eligible participants and lack of funding.

Patients will undergo a standard history and physical examination detailing objective clinical exam findings performed by one of the co-investigators. The research coordinator will obtain baseline values for intensity of pain, quality of life, and coping strategies. Baseline serum levels inflammatory markers will then be measured. Over the course of 12 weeks Thalidomide will be titrated as tolerated to achieve a minimum of a 30% reduction of pain on VAS from week 2.

Inclusion Criteria:

1. Age > 18 years
2. Histologically/laparoscopically confirmed endometriosis
3. Chronic pelvic pain defined as non-menstrual pain for at least two weeks in the previous month for at least 6 months
4. VAS of 6 or more at baseline
5. Failure, completion or intolerance of standard treatment modalities (oral contraceptive therapy, danazol, Depo-Provera, Depo-Lupron)
6. Patients must give written informed consent.
7. Patients must be willing and able to comply with the FDA-mandated S.T.E.P.S.® program.

Exclusion Criteria:

1. Pregnant and/or lactating female
2. Users of other angiogenesis inhibitors
3. Current use of Rifampin, rifabutin, barbiturates, glucocorticoids, phenytoin, carbamazepine, chlorpromazine, reserpine, penicillin derivatives, or St. Johns Wart in user of oral contraceptive therapy
4. Use of aromatase inhibitors, Etanercept (Enbrel), GnRH agonists (Depo-Lupron), and Danazol within the past 3 months
5. Use of norethindrone acetate (Aygestin) in the prior month
6. Seizure disorder
7. Hepatitis, or any active infection (upper respiratory infection, PID, etc)
8. History of thromboembolic disease.
9. Baseline neutropenia (ANC < 1000/mm^3)
10. Any severe physical or metal illness that would interfere with the completion of the protocol
11. Illicit drug or alcohol abuse