Inclusion Criteria:

1. Histologically or cytologically confirmed prostate carcinoma.

2. Evidence of metastatic disease on previous bone scan and/or CT scan and/or MRI.

3. Castrate-sensitive disease. Patients already on ADT are eligible as long as the time
from initiation of LHRH analog or antagonist is not greater than 1 month AND the
total exposure time to the LHRH analog or antagonist will not exceed 8 months (i.e.
the effectiveness of current depot LHRH analog or antagonist does not extend beyond 8
months since its initiation).

4. Patients who have received prior hormonal therapy are allowed to participate as long
as they have been off hormone ablation for 1.5 times as long as they were on it: e.g.
1) Patients who have received up to 4 months of hormonal ablation are eligible as
long as they have been off hormonal ablation for >/= 6 months; 2) Patients who have
received 1 year of hormonal ablation are eligible as long as they have been off
hormone ablation for >/= 18 months; 3) Patients who have received up to 2 years of
hormonal ablation are eligible as long as they have been off hormonal ablation for
>/= 3 years have elapsed since its discontinuation.

5. ECOG performance status
6. Patients must have normal organ and marrow function as defined below: a) WBC >/=
3000/uL; b) ANC >/= 1500/uL; c) Platelets >/= 100 x 10^3/uL; d) Hemoglobin >/= 9
g/dL; e) Creatinine metastases. For patients with liver metastasis ALT Bilirubin total bilirubin
7. Patients included in the study must be >/= 18 years old

8. Ability to understand and willingness to sign a written informed consent document.

Exclusion Criteria:

1. Autoimmune disease: Patients with a history of inflammatory bowel disease (including
Crohn's disease and ulcerative colitis) and autoimmune disorders such as rheumatoid
arthritis, systemic progressive sclerosis [scleroderma], Systemic Lupus Erythematosus
or autoimmune vasculitis [e.g., Wegener's Granulomatosis] are excluded from this
study.

2. Any underlying medical or psychiatric condition, which in the opinion of the
Investigator, will make the administration of study drug hazardous or obscure the
interpretation of AEs: e.g. a condition associated with frequent diarrhea or chronic
skin conditions, recent surgery or colonic biopsy from which the patient has not
recovered, or partial endocrine organ deficiencies.

3. Patients with known brain metastases.

4. Patients with small cell carcinoma of the prostate.

5. History of other malignancies, other than nonmelanoma skin cancer or Ta or T1 (low
grade) bladder carcinomas, unless in complete remission and off therapy for that
disease for at least 5 years.

6. Uncontrolled intercurrent illness including, but not limited to, ongoing or active
infection, history of congestive heart failure, unstable angina pectoris, cardiac
arrhythmia, or psychiatric illness/social situations that would limit compliance with
study requirements.

7. Known HIV, Hepatitis B, or Hepatitis C.

8. Untreated symptomatic spinal cord compressions.

9. Any non-oncology vaccine therapy used for prevention of infectious diseases (for up
to one month prior to or after any dose of ipilimumab).

10. Concomitant therapy with any of the following: IL-2, interferon or other non-study
immunotherapy regimens; cytotoxic chemotherapy; immunosuppressive agents; other
investigation therapies; or chronic use of systemic corticosteroids (used in the
management of cancer or non-cancer-related illnesses).

11. Previous participation in another ipilimumab clinical trial or prior treatment with a
CD137 agonist or CTLA-4 inhibitor or agonist.

12. History of acute diverticulitis, intra-abdominal abscess, GI obstruction, abdominal
carcinomatosis or other known risk factors for bowel perforation.

13. Patients who do not agree to practice appropriate birth control methods while on
therapy.

14. Concurrent use of 5-alpha reductase inhibitors (finasteride or dutasteride).