Pseudoangiomatous stromal hyperplasia (PASH) is an uncommon, benign mesenchymal lesion of the breast. Histologically, it is characterized by complex, anastomosing, empty, slit-like spaces that are lined by spindle cells in a dense collagenous stroma. We have evaluated 14 PASH cases morphologically and immunohistochemically, using antibodies against CD34 and progesterone receptor and reviewed the relevant literature. Also, we have evaluated the mast cell population of the lesions, using Giemsa stain. All of the cases were women presenting with a mass in the breast. The diameter of the lesions ranged from 1 cm to 13,5 cm (mean diameter 4 cm). The spindle cells, lining the slit-like spaces, were immunoreactive for anti CD34 whereas all were negative for anti progesterone receptor. The mean mast cell count was 17,5/10 HPF. Although differential diagnosis of PASH includes several mesenchymal lesions appropriate macroscopic sampling and immunohistochemistry are usually sufficient for proper diagnosis. Nevertheless, detection of immunostaining for CD34, using immunohistochemistry, may support the morphologic diagnosis.