Inclusion Criteria:

• Provide signed, written informed consent
• Have a diagnosis of AML according to World Health Organization (WHO) classification
• Relapsed after receiving up to 2 prior induction regimens (i.e. first or second relapse)or are refractory to not more than one prior combination chemotherapy induction regimen
• Be ≥ 55 years of age
• Have an ECOG score of 0-2
• Be able to comply with study procedures and follow-up examinations
• Be nonfertile or agree to use birth control during the study through the end of treatment visit and for at least 90 days after the last dose of study drug
• Have adequate liver and renal function as indicated by certain laboratory values

Exclusion Criteria:

• Received previous treatment with clofarabine
• Received bolus, intermediate or high-dose cytarabine as induction therapy unless certain remission criteria are met
• Have received a hematopoietic stem cell transplant (HSCT) within the previous 3 months
• Have moderate or severe graft versus host disease (GVHD), whether acute or chronic
• Are receiving any other chemotherapy or investigational therapy. Patients must have been off prior AML therapy for at least 2-4 weeks prior to entering study.
• Have a psychiatric disorder that would interfere with consent, study participation, or follow-up
• Have an active, uncontrolled infection
• Have any other severe concurrent disease, or have a history of serious organ dysfunction or disease involving the heart, kidney, liver, or other organ system
• Have been diagnosed with another malignancy, unless disease-free for at least 5 years; patients with treated melanoma skin cancer, in situ carcinoma, or cervical intraepithelial neoplasia, regardless of the disease-free duration, are eligible for this study if definitive treatment for the condition has been completed; patients with organ-confined prostate cancer with no evidence of recurrent or progressive disease are eligible if hormonal therapy has been initiated or the malignancy has been surgically removed.
• Have clinical evidence suggestive of central nervous system (CNS) involvement with leukemia unless lumbar puncture confirms absence of leukemic blasts in the cerebrospinal fluid(CSF)
• Known HIV positivity
• Are pregnant or lactating