Adult granulosa cell tumors (AGCTs) have a heterogeneous morphology and an unpredictable behavior, which can lead to a misinterpreted diagnosis. The aim of our study was to assess the immunoexpression of estrogen receptor (ER) alpha, Ki67, calretinin, and inhibin A in AGCTs, in order to evaluate their value in diagnosis and prognosis of this type of tumor. Immunohistochemical stainings for these markers were performed in 21 cases of AGCTs. The immunopositivity evaluation of calretinin and inhibin A was scored according to the percentage of staining intensity and the extent of positive cells, of ER alpha was scored based on the percentage of positive cells, and Ki67 score was recorded as the percentage of positively stained nuclei across the tumor, without taking in consideration the staining intensity. ER was positive in nine cases, Ki67 was expressed in 12 cases, calretinin showed positive immunoreactivity in 16 cases, and inhibin A was positive in 14 cases. Stromal cells presented also immunopositivity for inhibin A and calretinin in the negative cases. ER alpha and calretinin immunoexpression can help in identification of cell components of AGCT. Our results regarding Ki67 expression emphasize the potential utility of this marker in tumor behavior prediction. Inhibin A immunopositivity has an important value in AGCT diagnosis, in association to the other evaluated markers. Additional studies are needed to identify new specific and sensitive markers for AGCT or, at least, of a panel of markers which might contribute to a more accurate characterization of these tumors.