The review discusses the role of history, general examination and different modalities of investigation in diagnosis of obstructive sleep apnea. Obstructive sleep apnea is defined as a condition caused by either occlusion (apnea) or partial collapse (hypopnea) upper airway despite the presence of simultaneous respiratory effort. Snoring, excessive daytime sleepiness and obstructive episodes are the most common clinical features of obstructive sleep apnea. Important aspects of the examination in patient's obstructive sleep apnea include general appearance, weight, craniofacial morphology, nacal airway, tongue size, soft palate and uvula. Lateral cephalometry is useful as screening test for anatomical abnormalities in-patients having obstructive sleep syndrome. Computerized topography and acoustic pharyngomertry represent a non invasive technique that allows to localizing the site of airway obstructive. .Polysomnography is the Process by which sleep is recorded and analyzed based on variable number of physiological parameters. Treatment of obstructive sleep apuea may be non-surgical or surgical.