Obstructive sleep apnea syndrome (OSAS) is characterized by the development of repeated episodes of pharyngeal collapse. Respiratory movements attempt to reopen the closed pharynx leading to resumption of ventilation associated with micro-arousals. Three kinds of measurements are needed to establish the diagnosis of OSAS: airflow (reduction or complete interruption), respiratory effort in response to increased airway resistance, micro-arousals associated with the end of the respiratory event. Classically, polysomnography was used to establish sleep architecture using electroencephalography, electromyography and electro-oculography. Air flow was measured by thermistors, chest and abdominal movements and oximetry were monitored. Other more accessible methods can also be used to establish reliable diagnosis. Measuring pulse transit time using ECG and oximeter sensors provide a semi-quantitative measurement of respiratory effort. Likewise, cardiovascular markers (heart rate, blood pressure, pulse time) can be used instead of electroencephalography to establish the arousal pattern. Cardiovascular markers are as sensitive and probably as specific as EEG for identifying micro-arousals. Measuring nasal pressure provides a much less invasive quantitative assessment of airflow than pneumotachography. The shape of the inspiratory signal is also an indirect marker of respiratory effort. These new tools can be used to characterize the three elementary abnormalities observed in OSAS: variations in airflow, increased respiratory effort, fragmented sleep, using a very simplified setting compared with classical techniques. Therapeutic monitoring of OSAS patients, particularly after surgery, should not be limited to physical examination known to lack sufficient sensitivity. It should also include simplified methods or complete polysomnography to obtain a precise measurement of residual respiratory events and sleep pattern after treatment.