This chapter describes the case of a 7.5-month-old Caucasian infant with a birthweight of 3.9 kg, born full term to a 35-year-old mother. It presents the clinical history, examination, follow-up, treatment, diagnosis, and the results of the procedures performed on the patient. The patient's pediatrician suspected an upper respiratory tract infection and treated her with "Infants' Cold Formula" with no relief. A soft-tissue X-ray of her neck revealed hypertrophy of her adenoids, which were obstructing the nasal airway. There was paradoxical inward rib-cage motion during inspiration throughout much of the study. Tachypnea was present, particularly during REM sleep. The diagnosis based on the polysomnography (PSG) results was severe obstructive sleep apnea (OSA), pediatric. The patient's symptoms and O2 saturation improved immediately thereafter. A follow-up sleep study 2 months later revealed that the patient no longer demonstrated an obstructive breathing pattern or impairment in gas exchange.