Controls of respiration have different settings during sleep than during wakefulness. Respiration will also be influenced by sleep state organization and circadian rhythm. Polygraphic monitorings in infants and children must take into account the timing of the longest sleep and longest wakeful periods and the distribution of sleep states. Attention must be given not only to "apneas" and blood gas changes monitored noninvasively but also to breathing frequency, upper airway resistance, and the impact of respiratory changes on the cardiovascular system and sleep continuity. Respiratory efforts and upper airway resistance are responsible for important mechanical intrathoracic changes, which must be evaluated, since they have clinical consequences. For example, infants with an apparent life-threatening event may have an unrecognized increase in upper airway resistance long before having a mixed or obstructive sleep apnea. Muscle disorders in young children require regular sleep monitoring whose results will strongly influence therapeutic approaches. Therapy may change over time, depending on the prominence of the inspiratory muscle weakness or the importance of the mandibular abnormalities induced by the muscle disorder and its impact on upper airway resistance during sleep. At times, it is difficult to avoid sleep disturbances with aggressive investigation of breathing during sleep, and several successive days of monitoring may be needed to determine sleep-related pathology.