Patients are referred to departments for plastic surgery increasingly frequently for breast reconstruction following mastectomy for cancer of the breast. Successful results depend greatly on the primary mastectomy carried out by surgeons without experience in reconstruction. It is particularly important that the incisions are suitably placed so that the final result can be satisfactory. Our material consists of 119 patients who had been submitted to unilateral mastectomy for cancer of the breast at least one year previously. One fifth of the patients had hypertrophic breasts. The unequal distribution of weight following unilateral mastectomy is followed by such considerable discomfort from the remaining breast that this alone makes a reduction plastic operation necessary. Simultaneously, reconstruction is carried out on the side of the mastectomy. As the method of reconstruction, introduction of silicone prosthesis were carried out in 110 patients. Nine patients were, in addition, submitted to more complicated plastic flap procedures. The postoperative course was uncomplicated in 112 patients (94%). Reoperation proved necessary on seven occasions; in four patients on account of haematoma formation and rupture of the wound in three patients. In four patients, the prosthesis had to be renewed on account of rupture during the subsequent years. Guidelines for placing the incisions at the primary mastectomy are suggested to facilitate successful reconstruction. Finally, a suitable biopsy technique is described.