Findings on mammography resulted in a change of treatment policy in 17 of 200 patients with small breast cancers (T1/T2 less than 4 cm, N0/N1, M0). Twelve patients were considered unsuitable for conservation therapy because of mammographic evidence of either extensive in situ carcinoma or more than one focus of invasive carcinoma. These patients were treated by mastectomy and histology confirmed widespread in situ carcinoma or multifocal/multicentric invasive carcinoma. Seven patients were found to have unsuspected contralateral lesions on mammography, of which five were subsequently shown to be malignant. Routine preoperative mammography is essential in the management of patients with small breast cancers.