The maintenence of normal skeletal metabolism is dependent on mechanical factors, such as muscle pulls and weight bearings. When these factors are removed, bone mass decreases and osteoporosis ensues. There have been several reports about the reduction of bone mass in long bone fractures. However, radiographical classification of the osteoporosis, following tibial fracture, has been published rarely in domestic or foreign countries. So we studies 100 tibial fracture with minimum immobilization of eight weeks (average, 16 weeks), following either a closed redution or an open reduction between January 1987 and November 1989. One hundred patients (100 tibiae), were divided into 3 groups according to the age:below 20 years;21 to 40 years;and over 41 years, and radiographs were taken bimonthly to observe the patterns, the time of occurrence and disappearance of disuse osteoporosis in tibial fractures. The results were as follow:l. Among the various radiographic patterns of disuse osteoporsis, the incidence of uniform osteoporosis was highest (68%) and that of band-like osteoporosis was the next (31%). 2. Uniform osteoporsis seemed to occur more frequently in older age group:92% in over 41 years group, 70% in 21 to 40 years group, and 26% in below 20 years group. 3. Band-like osteoporosis was observed mostly in 21 to 40 years group (42%), secondly in below 20 years group, and leastly in over 41 years group (16%). 4. Posttraumatic disuse osteoporosis in tibial fractures appeared first in the below 20 years group (average 7.3 weeks), and second in the 21 to 40 years group (average 8.2 weeks), and last in the over 40 years group (average 9.1 weeks). 5. Nine tibiae (39%), in below 20 years group, did not have any radiographic patterns of disuse osteoporosis and all nine patients were under 13 years old. 6. Band-like osteoporosis disappeared in average 32 weeks, and uniform osteoporosis continued over 40 weeks in 25 of the 39 tibiae (64%). 7. Uniform osteoporosis appeared more in conservative treatment group (46/68), and band-like osteoporosis appeared more in operative treatment group (19/31).