Statement of the Problem: Fibro-osseous lesions (FLs), may rarely exhibit malignant features likewise undergo malignant transformation. Awareness of these features can assist in screening for potentially malignant cases and identifying low-grade central osteogenic sarcoma (LGCOS) that may mimic FLs.Purpose: The objective of this study was to determine the usability of an index in predicting malignant changes in jaw FLs.Materials and Method: This was a retrospective study where hematoxylin and eosin (H&E) slides and archival records of fibrous dysplasia (FD) and ossifying fibroma (OF) cases were reviewed. The sections were assessed for permeation of marrow spaces, stromal growth pattern, cytologic atypia, mitotic activity, and pattern of bone growth, which are parameters for diagnosing LGCOS. The predictive histologic index of malignancy (PHIM) was determined by a sum of the scores and graded as 0=nil, 1=low, 2 & 3=moderate, and 4 & 5=high. Data were presented using descriptive analysis.Results: Ninety-three cases of FLs met the inclusion criteria, consisting of 40(43%) cases of FD and 53(57%) cases of OF. The peak age of presentation for FD and OF was 2nd and 3rd decade. There was a female preponderance of 1:1.6. The maxilla was the most common site affected by FD, while the mandible was most commonly affected by OF. For FD cases, the PHIM was moderate in 10(25%) cases and low in 21(52.5%) cases. Similarly, for OF cases, 30(56.6%) cases had low grade PHIM while 10(17%) cases had moderate grade PHIM.Conclusion: The PHIM depicted low to moderate malignancy grade in some of the cases studied. Follow up studies would be necessary to assess the PHIM.