Purpose : To evaluate prognostic factors for arthritis and usefulness of bone SPECT in reconstructed joint. Material & method : ACL reconstruction using bone-patellar tendon-bone graft was performed in fourteen patients from March 1996 to March 1997, and follow-up bone SPECT was done. The mean duration from ACL reconstruction to SPECT was 23 months. The knee was defined to be unstable when the difference of displacement measured using KT-2000 arthrometer was greater than 3 ㎜. Lesions were evaluated in sub-divided five compartments ; patello-femoral joint, anteromedial, anterolateral, postero-medial and posterolateral compartment of tibio-femoral joint. Result : Geographic bone bruise was found in 9 cases(15 compartments) of 14 patients and bone SPECT revealed increased uptake in all the compartments. Reticular type bone bruise was found in 6 cases(7 compartments) and no compartment revealed increased uptake. Partial meniscectomy was done in 9 cases(16 compartments), and 8 cases(13 compartments) of them revealed increased uptake. Six cases were unstable and four of them revealed increased uptake in the patello-femoral joint. Activity level was not correlated with hot uptake. Conclusion : Bone SPECT is a useful method to predict osteoarthritis after ACL reconstruction. Geo-graphic bone bruises at injury, meniscectomy and instability are important factors for prognosis after ACL reconstruction.