Inclusion Criteria:

          -  Patients with one of the following diagnoses:

               -  Relapsed or primary refractory acute myeloid leukemia (AML), including

                    -  Patients with relapsed AML after allogeneic stem cells transplantation,
                       including those who have received donor lymphocyte infusions

                    -  Isolated central nervous system (CNS) or extramedullary disease

                    -  Note: a response monitoring plan must be developed a priori for subjects
                       with extramedullary disease

               -  Myelodysplastic syndrome

                    -  >= 10% blasts, including patients who have received prior hypomethylating
                       agents

          -  Karnofsky or Lansky performance scale (PS) greater or equal to 70

          -  Serum creatinine =< 2 mg/dl or creatinine clearance greater or equal than 40 cc/min.
             Creatinine for pediatric patients =< 2 mg/dl or =< 2 times upper limit of normal for
             age (whichever is less)

          -  Forced expiratory volume in one second (FEV1), forced vital capacity (FVC) and
             diffusion capacity of the lung for carbon monoxide (DLCO) >= 50% of expected,
             corrected for hemoglobin. For pediatric patients, if unable to perform pulmonary
             function tests (most children < 7 years of age), pulse oximetry >= 92% on room air by
             pulse oximetry

          -  Total bilirubin =< 2 mg/dl or =< 2.5 x upper limit or normal (ULN) for age (unless
             Gilbert's syndrome)

          -  Serum glutamate pyruvate transaminase (SGPT) (alanine aminotransferase [ALT]) =< 2.5 x
             ULN for age

          -  Left ventricular ejection fraction >= 40%

          -  Patients with seizure disorder may be eligible if seizures well controlled

          -  Negative serum test to rule out pregnancy within 2 weeks prior to enrollment in
             females of childbearing potential (non-childbearing potential defined as premenarchal,
             greater than one year post-menopausal, or surgically sterilized)

          -  Sexually active males and females of childbearing potential must agree to use a form
             of contraception considered effective and medically acceptable by the investigator

          -  Ability to understand and willingness to sign the written informed consent document

          -  Negative serology for human immunodeficiency virus (HIV)

        Exclusion Criteria:

          -  Investigational therapies in the 2 weeks prior to beginning treatment on this protocol

          -  Any comorbidities that in the opinion of the investigator will preclude receiving
             fludarabine, decitabine or cytarabine

          -  Uncontrolled infection, defined as an infection which has not resolved spontaneously
             or does not show evidence of significant resolution after initiating appropriate
             therapy. Asymptomatic viremia such as cytomegalovirus (CMV), human papillomavirus
             (HPV), BK virus, hepatitis C virus (HCV), etc. is NOT considered as an exclusion
             criteria

          -  Uncontrolled arrhythmias or uncontrolled symptomatic cardiac disease

          -  Active graft versus host disease (GVHD)

          -  Patient on corticosteroids to control GvHD