Pseudoangiomatous stromal hyperplasia (PASH) is often a microscopic incidental finding in breast biopsies performed for benign or malignant diseases. In rare cases, it presents as a localised breast mass. Since Vuitch et al first described this condition in 1986, only 109 cases of PASH presenting as a palpable or mammographically detectable mass have been documented. PASH is characterised by a dense, collagenous proliferation of mammary stroma, forming inter-anastomosing capillary-like spaces. It is important to distinguish this benign lesion from a low-grade angiosarcoma. Here we describe the clinical, radiological and histological features of a very unusual case of PASH that presented as a rapidly growing breast lesion in a 37-year old woman.