We report the first case in the medical literature of a pneumothorax complicating fine needle aspiration cytology (FNAC) of a breast lump in a woman with a mild form of Poland's syndrome. The pneumothorax was treated conservatively. This is the first case of breast FNA-related pneumothorax seen in our clinical practice. We believe that the absence of pectoral muscles has increased the risk of this complication. We have also diagnosed an incidental screen-detected breast cancer affecting the ipsilateral breast in the same patient. We conclude that caution should be exercised when performing FNAC of breast lesions in patients with Poland's syndrome. The procedure should be preferably performed under image guidance in such patients in order to minimise the risk of this complication.