The obstructive sleep apnea/hypopnea syndrome (OSA/H) is characterised by repetitive obstruction of the upper airway during sleep. The consequences of OSA/H include excessive daytime sleepiness, reduced perceived health quality and an increased risk of driving accidents. There is evidence that treatment with nasal continuous positive airway pressure (CPAP) is effective in eliminating these consequences. In addition, OSA/H may also be associated with hypertension and an increased risk of vascular disease, and although there is no clear evidence in this regard, CPAP may be effective alleviating these consequences as well. Nasal CPAP is considered the treatment of choice for clinically significant OSA/H. The optimal CPAP prescription is that which is most effective in eliminating the adverse consequences of OSA/H. Patients should be initially treated with standard CPAP. For those in whom standard CPAP is unsuccessful or intolerable bi-level or self-adjusting modes may be attempted. The nasal CPAP pressure level can be titrated to eliminate apnea, hypopnea, snoring, respiratory arousal and inspiratory flow limitation as a means of predicting successful long-term therapy. The reliability of these physiologic parameters in predicting the optimal long-term CPAP pressure is eroded by the tendency of CPAP pressure-level requirement to decrease with chronic CPAP use, and by other factors that may increase the CPAP pressure requirement. The split-night polysomnogram and unattended auto-CPAP titration have been proposed as efficient means of determining the optimal CPAP pressure, but for patients with subtle OSA/H, underlying cardiopulmonary disease or other forms of sleep-disordered breathing a full-night polysomnogram may be required. The CPAP prescription must include a comfortable well-fitting interface. When CPAP is prescribed it is essential that the patient undergo clinical re-evaluation to ensure that treatment goals are being met.