Objective: The purpose of this study is to investigate the in vivo magnetic resonance spectroscopic (MRS) features of pelvic lesions using long echo time and to characterize the spectral patterns of various pathological entities. Materials and Methods: 17 patients with surgically and histopathologically confirmed pelvic lesions underwent long echo-time MRS, and the results obtained were analyzed. Before laparotomy, choline (Cho), lactate, lipid and creatine (Cr) levels of all lesions were measured by single voxel MRS ( point-resolved spectroscopy technique, TE 136 ms). Voxels were placed in the center of the lesions. The MRS results of lesions were compared with the final histopathological diagnoses. Results: Spectroscopy analysis of serous, mucinous and undifferentiated carcinoma of the ovary revealed Cho, lactate and lipid signals, but granulosa-theca cell tumor showed only a lipid signal. The Cho signal was obtained from only 3 patients with mature cystic teratoma but none of the other benign ovarian tumors and pelvic abscesses. A lipid signal was detected in 3 patients diagnosed with pelvic abscess and all benign ovarian tumors. In addition to the lipid signal, a lactate signal was detected in the spectra of two pelvic abscesses. One case of endometrioma and 1 case of teratoma did not show any signal. Conclusion: MRS demonstrates significant differences in metabolite concentration between benign and malignant ovarian tumors and pelvic abscesses. MRS may therefore be helpful in the differential diagnosis of adnexal lesions. Copyright (C) 2005 S. Karger AG, Basel.