Inclusion Criteria:

- Patients with a prior diagnosis of a pediatric malignancy (brain tumors, solid
tumors, leukemia/lymphoma) who are in remission, and are > 3 years from initial
diagnosis. Patients must have completed therapy a minimum of 6 months prior to study
entry.

- Patients must have English as their primary language

- Patients must be >3 and less than or equal to 16 at the time of study enrollment

- Patients must fulfill the operational criteria for neurocognitive deficit and have
an IQ > 50.

- Patients must be currently enrolled in a school or a learning environment where an
adult familiar with the child's academic performance can provide ratings of that
performance over the time of the trial.

- Patients must have wbc, hemoglobin and platelet parameters which fall within the
norms for the patient's age.

- Patients must have adequate hepatic function (bilirubin less than or equal to 1.5
mg/dl and SGPT < 5x normal) and renal function (normal Cr for age/GFR greater than or
equal to 70 ml/min/1.73m2)

- Patients must be able to swallow gel caps.

- Signed informed consent must be obtained according to institutional guidelines. When
appropriate the patient will be included in all discussion in order to obtain verbal
assent.

- Protocol and informed consent must be approved by the local IRB prior to any patient
registration and reapproved every 12 months.

Exclusion Criteria:

- Patients who have evidence of a significant neurological abnormality prior to their
cancer diagnosis that would affect neuro-behavioral development (such as genetic:
Fragile X, Downs syndrome, or acquired disorders: closed head injury)

- Patients with a prior (pre-cancer) diagnosis of attention deficit hyperactivity
disorder or major depression

- Patients who have a medical condition which would preclude the use of clonidine
(medicated for hypertension, cardiac conduction disturbances, cerebrovascular
disease, or chronic renal failure)

- Patients must not have received psychotropic medication (SSRIs, methylphenidate),
anxiolytics, or hypnotics within 2 weeks of study entry.

- Patients who are receiving concurrent scheduled barbiturates or sedating drugs.

- Currently (within 6 months) known to abuse drugs or to be dependent on any drug
including alcohol or with a positive urine drug screen.

- Women of childbearing age must not be pregnant or lactating. This group is excluded
because of teratogenic potential of this agent demonstrated in rat and rabbit models.