Abstract The aim of this study was to evaluate the immunohistochemical expression of receptor activator of nuclear factor kappa-B ligand (RANKL) and of osteoprotegerin (OPG), important proteins correlated with osteoclastogenesis, in central giant cell lesions (CGCL) and peripheral giant cell lesions (PGCL) and to compare their expression with the histological and clinical parameters for quantification of multinucleated giant cells (MGC) and their nuclei, lesion size, and recurrences. Twenty cases of each lesion type were selected to quantify the number of MGCs and nuclei/mm2 of connective tissue. The immunoreactivity of RANKL and OPG was expressed as a percentage of the marked area in the stroma. Clinical data were collected from pathoanatomical and medical reports. No statistical differences were found for the number of MGCs (p = 0.24) between PGCL and CGCL, but the number of nuclei within the MGCs was higher in CGCL (p = 0.01). RANKL expression was higher in CGCL than in PGCL (p = 0.04) and all recurrent lesions showed higher RANKL and OPG expressions than nonrecurrent lesions. We report higher RANKL expression and a greater number of nuclei in CGCL, which may explain the difference in clinical behaviour between these lesions and their pathogenesis.