Background and Objective:  The origin of cells in the mature periodontium, and the location of their progenitors, are still unknown. It is also unknown whether inflammation influences the number and distribution of these cells within the periodontium. Molecules such as STRO‐1, CD146 and CD44 have been identified on a variety of mesenchymal stem cells. The aim of this study was to identify and localize putative stem cells in diseased and healthy human periodontal ligament using cell‐surface markers for mesenchymal stem cells.Material and Methods:  Healthy and periodontitis‐affected teeth were collected, fixed in 10% neutral‐buffered formalin, decalcified and embedded in paraffin in preparation for immunohistochemistry. Antibodies against STRO‐1, CD146 and CD44 were used to identify putative stem cells in the periodontal ligament.Results:  Putative stem cells were identified in both healthy and diseased periodontal ligament. They were mainly located in the paravascular region and small clusters of cells were also found in the extravascular region. Wider distributions of these cells were detected in sections of diseased ligament.Conclusion:  Within the periodontal ligament of both healthy and diseased teeth, cells have been identified consistent with their identification as putative stem cells. The presence of an inflammatory reaction associated with periodontitis may enhance the number of these cells.