【Abstract】 Objective To explore the correlation between pain grading, stage of necrosis and bone marrow edema(BME) in nontraumatic osteonecrosis of femoral head (NONFH) so as to strengthen understandings about cl inical significance of BME in NONFH. Methods From October 2004 to October 2006, 97 patients (149 hips) with NONFH were treated. There were 68 males and 29 femals with an average age of 38.8 years (19-62 years). The disease course was from 20 days to 4 years. BME was identified grade 0 to grade 2 according to MRI. Based on grading scale of pain, pain grading were divided into no pain (grade 0), mild pain (grade 1) and moderate or severe pain (grade 2). According to Association Research Circulation Osseous staging system, NONFH were divided into I-IV stages. The incidence rate of BME in each pain grading and stages of necrosis was analyzed respectively. Contingency table analyses and rank sum tests were used to compare the difference of pain grading and stages of necrosis among these groups. Results The total incidence rate of BME was 73.15% (109/149), the incidence rateswere 84.38% in pain groups (108 /128) and 94.12% in the grade 2 (32/34). Pain grading correlated with BME rating (P lt; 0.001).The results of rank sum tests for several independent samples showed significant difference in BME among pain groups(P lt; 0.001). With the advance of pain scale, the mean rank of BME increased gradually(28.19 for grade 0, 78.94 for grade 1 and 96.12 for grade 2). BME was more commonly and clearly seen in stage Ⅱ（77.05%）and stage Ⅲ（82.81%）of NONFH. Stage I-III of NONFH correlated with BME rating (P lt; 0.001). The results of rank sum tests showed significant difference in BME rating among three stages (P lt; 0.001). With the advance of disease, the rank of BME rating increased gradually (39.07 for grade 0, 60.16 for grade 1 and 86.15 for grade 2 ). Conclusion BME is a sign that is accompanied with NONFH. The probabil ity and extent of BME correlated well with the pain and stage of NONFH．The condition of BME can be used as a index for the appraisal of advancement of disease and the judgment of treatment result.