The relationship between sinonasal disease and septal deriations is well known, albeit vaguely. There was no serious attempt to classify deviations except calling them mild deviations, gross deviations, spur; high deviations, etc. The airflow changes in these deviations, which lead to mucosal changes predisposing to polyps or infection have not been documented clearly. In this study we made a classification of septal deformities by modifying the classification described by Mladina in 1987. This classification has been applied to 100 consecutive cases who have been advised nasal surgery and 100 normal individuals who did not have any nasal symptoms. All patients had CT scan of PNS and their CT findings were studied in relation to the type of deviation. This paper presents an analysis of the incidence of various types of deviations in patients and controls and the relationship of different deformities to the sinus pathology.