Purpose: the objective was to assess the efficacy of fast spin-echo (FSE) imaging in the detection of articular cartilage abnormality in osteoarthrosis of the knee Material and Methods: We studied 356 articular surfaces in 73 knees that had been examined by both MR imaging and arthroscopy. the MR images were obtained with FSE imaging (TR/TE 4200/100) on a 0.5 T unit. the surface abnormalities of the articular cartilage that were detected by MR imaging were compared with the arthroscopic findings Results: the overall sensitivity and specificity of MR in detecting chondral abnormalities were 60.5% (158/261) and 93.7% (89/95) respectively. MR imaging was more sensitive to the higher grade lesions: 31.8% (34/107) in grade 1; 72.4% (71/98) in grade 2; 93.5% (43/46) in grade 3; and 100% (10/10) in grade 4. the MR and arthroscopic grades were the same in 46.9% (167/356), and differed by no more than 1 grade in 90.2% (321/356) and 2 grades in 99.2% (353/356). the correlation between arthroscopic and MR grading scores was highly significant with a correlation coefficient of 0.705 ( p<0.0001) Conclusion: FSE sequence was less sensitive to mild cartilage abnormality but useful in detecting moderate to severe abnormality and in evaluating the degree of articular cartilage abnormality