To identify the clinical value of pre-operative ipsilateral mammography in patients with Paget's disease of the breast. The mammograms and histological data of 27 patients with Paget's disease and 60 patients with symptomatic DCIS without Paget's disease were reviewed and compared. Forty-four percent of patients with Paget's disease had normal mammograms. Mammography did not discriminate between DCIS and invasive disease, and could not predict DCIS sub-type. DCIS was large cell in 80% of patients with Paget's disease. Given that large cell DCIS in non Paget's patients is normally visible mammographically, the large proportion of Paget's patients with normal mammography is difficult to explain, but could be due to the small size of the lesions. Comparison of the Paget's and non-Paget's groups showed that large cell solid disease was more common, small cell cribriform less common and normal mammography more common in the Paget's group. Given that mastectomy is the treatment of choice, the only clinical value of ipsilateral mammography in our unit would be to allow image guided core biopsy of any detected mammographic abnormalities to determine the presence of invasive disease prior to surgery, thus indicating the need for node sampling pre-operatively rather than as a delayed procedure. This study also confirms that mammography is of little help in deciding if breast conserving surgery is appropriate for individual cases of Paget's disease of the nipple due to the insensitivity of mammography in showing the site of disease.