Identification of phenotypes and endotypes contributes to a better understanding of the complex pathophysiology and heterogeneous clinical presentation of obstructive sleep apnea. The general goal of this dissertation was to determine the added value of the identification and use of potential predictors; risk factors associated with obstructive sleep apnea and factors influencing treatment outcome. By identifying predictors, the specificity and sensitivity of diagnostic tools can be increased. In addition, these predictors can provide guidance in choosing from the treatment options, which could subsequently lead to an increase in treatment success. The phenotypes studied in this dissertation are: snoring sound, dental parameters and positional dependency. The predictive value of specific manoeuvres and tools during sleep endoscopy for treatment success with a mandibular repositioning device was also studied. Finally, the innovative treatment for obstructive sleep apnea, hypoglossal nerve stimulation was investigated.