Inclusion Criteria:

- Have a diagnosis of ALL and confirmed by pathologic assessment.

- Be ≤ 21 years old at time of initial diagnosis.

- Eligible patients must have: Primary refractory disease; OR relapsed or refractory
disease after a minimum of 2 prior blocks of treatment.

- Must not be eligible for therapy of higher curative potential.

- Have a Karnofsky Performance Status of ≥ 50 or Lansky Performance Scale of ≥ 30.

- Provide a signed, written informed consent from parent or guardian or young adult
patients.

- Be able to comply with study procedures and follow-up examinations.

- Have adequate cardiac function without treatment.

- Have adequate organ function as indicated by the laboratory values for serum
creatinine, serum bilirubin, AST and ALT, obtained within 7 days prior to
registration.

Exclusion Criteria:

- Received previous treatment with clofarabine.

- Patients with isolated extramedullary disease.

- Have received prior BMT or PBSCT within the last 6 months.

- Have received prior BMT or PBSCT more than 6 months ago, but now has compromised
organ function.

- Have an active, uncontrolled systemic infection.

- Are pregnant or lactating. Male and female patients who are fertile must agree to
use an effective means of birth control to avoid pregnancy.

- Have a psychiatric disorder that would interfere with consent, study participation,
or follow-up.

- Have received any other chemotherapy within the previous 2 weeks and must have
recovered from acute toxicity oa all previous therapy prior to enrollment.

- Have any other severe concurrent disease.

- Have recent history of significant renal, hepatic or pulmonary dysfunction, or
cardiac dysfunction or on treatment to support cardiac function.

- Have CNS disease.