BACKGROUND: The literature on variations of rib is limited. Very little has been written in the radiological journal of this country on the subject. It seemed of interest to investigate the nature and incidence of congenital variations in a series of routine chest roentgenograms. The topic of rib variations has not been covered extensively in the radiological journals in Korea. This has presented an opportunity to investigate the nature, type, shape and incidences of congenital rib variations in normal Korean adults from a series of routine roentgenograms. METHODS: Chest radiographs of 5,000 adults (,) who visited our hospital for a routine check-up or for employment physical examinations from January 1996 to September 1998, were consecutively reviewed. The sex distribution consisted of 2,827 male males and 2,173 females (ratio of 1.3:1) with the age range between 19 and 65 years (mean age: 34.6 years). The chest PAs was were analyzed for the presence, type, location, and shape of the rib variations (.) From this data, and we the incidence of each type of variations was calculated. RESULTS: Seventy-six of the 5000 adults (1.52%), 63 male (2.23%) and 13 female (0.6%), showed 88 cases of rib variation (Table 1). Bifid rib (n=35) was the The most common variation was the bifid rib (n=35), followed by hypoplasia of the rib (n=22), flaring of the rib (n=18), bridging of the ribs (n=7), cervical ribs (n=3), and fusion of between ribs (n=3) (Table 2). (New paragraph)Bifid The bifid rib (Table 1) was found most frequent in the right fourth rib (12/35, 34.3%), followed by the left fifth rib (6/35, 17.1%) and right third rib (6/35, 17.1%). Hypoplasia of the rib was common in first rib (20/22, 90.9%). Flaring of the rib was common at fourth rib (8/18. 44.4%, right and left combined) (,) and bridging between ribs was common between first and second rib (3/7, 42.9%). CONCLUSION: The percentage of incidence of rib variations in adults was 1.52%. Bifid rib was the most common variation, followed by hypoplasia, flaring, bridging, cervical rib, and fusion of ribs(,) in decreasing order.