Inclusions Criteria:

• written informed consent/assent is obtained
• meet minimal criteria established by the International Classification of Sleep Disorders (ICSD) manual of the American Academy of Sleep Medicine (AASM) for narcolepsy (or presumed narcolepsy) or OSAHS OR have a previous diagnosis of narcolepsy or OSAHS before the screening visit
• have a complaint of ES
• are in good health as determined by a medical and psychiatric history, physical examination, ECG, and clinical laboratory tests
• have blood pressure values greater than those for the 5th percentile and less than the 95th percentile on the National High Blood Pressure Education Program guidelines for blood pressure levels for boys and girls ages 6 to 16 years
• girls who are postmenarche or sexually active, have a negative urine pregnancy test at screening, must be using a medically acceptable method of birth control, and must agree to continue use of this method for the duration of the study (and for 2 cycles after participation in the study); acceptable methods of birth control include: barrier method with spermicide; steroidal contraceptives (oral, transdermal, implanted, or injected) in conjunction with a barrier method; intrauterine device (IUD); or abstinence
• able to swallow a tablet similar in size and shape to the study drug tablet
• negative urine drug screen (UDS) for any illicit drug, alcohol (ethanol), stimulants at screening; if positive for stimulants (prescribed for excessive sleepiness) at screening, UDS to be repeated after a washout period and before baseline
• have a parent or legal representative who is willing to participate in the study

Exclusion Criteria: Patients are excluded for participating in this if 1 or more of the following criteria are met:

• have self-induced sleep deprivation/poor sleep hygiene
• have a past or present seizure disorder (except history of single febrile seizure), a history of psychosis, or of clinically significant head trauma (eg, brain damage) or past neurosurgery
• have a history of suicide attempt, or are at suicidal risk
• a clinically significant drug sensitivity to stimulants such as amfetamine, dexamfetamine, or methylphenidate; and/or modafinil or any of its components
• use of any monoamine oxidase (MAO) inhibitors or selective serotonin reuptake inhibitors (SSRIs) within 2 weeks of the baseline visit (NOTE: SSRIs will be allowed for cataplexy if the patient has been on a stable dose for atleast 1 month.)
• received any investigational drug (except modafinil) within 4 weeks of the baseline visit
• any disorder that could interfere with drug absorption, distribution, metabolism, or excretion (including previous gastrointestinal surgery)
• active, clinically significant gastrointestinal, cardiovascular, hepatic, renal, hematologic, neoplastic, endocrine, neurologic, immunodeficiency, pulmonary, or other major clinically significant disorder/disease
• any clinically significant deviation from the normal range(s) in the physical examination or ECG findings, or clinical laboratory test results (ie, serum chemistry, hematology) at the screening or baseline visit
• absolute neutrophil count (ANC) below the lower limit of normal at screening (NOTE: If the ANC is below the lower limit of normal at the baseline visit, the medical monitor will be consulted for continued eligibility in the study.)
• seated pulse outside the range of 60 to 115 bpm after resting for 5 minutes
• a history of alcohol, narcotic, or any other substance abuse or dependence as defined by the Diagnostic and Statistical Manual of the American Psychiatric Association, 4th Edition (DSM-IV) criteria
• a total daily intake of more than 500mg of caffeine per day (eg, approximately ten 330-ml cans of caffeinated soft drinks, 5 cups of coffee or tea, or about 750g of chocolate per day) within 1 week of the baseline visit
• pregnant or lactating/nursing girl; any girl who becomes pregnant during the study will be withdrawn
• a clinically significant illness within 4 weeks of the baseline visit; or is symptomatic for any clinically significant illness at the baseline visit