Purposes. The present paper reports clinical cases where nummular eczema developed during the course of breast reconstruction by means of implantation and evaluates the occurrence patterns and ratios of this complication. Methods. 1662 patients undergoing breast reconstruction were reviewed. Patients who developed nummular eczema during the treatment were selected, and a survey was conducted on these patients regarding three items: (1) the stage of the treatment at which nummular eczema developed; (2) time required for the lesion to heal; (3) location of the lesion on the reconstructed breast(s). Furthermore, histopathological examination was conducted to elucidate the etiology of the lesion. Results. 48 patients (2.89%) developed nummular eczema. The timing of onset varied among these patients, with lesions developing after the placement of tissue expanders for 22 patients (45.8%); after the tissue expanders were replaced with silicone implants for 12 patients (25%); and after nipple-areola complex reconstruction for 14 patients (29.2%). Nummular eczema developed both in periwound regions (20 cases: 41.7%) and in nonperiwound regions (32 cases: 66.7%). Histopathological examination showed epidermal acanthosis, psoriasiform patterns, and reduction of sebaceous glands. Conclusions. Surgeons should recognize that nummular eczema is a potential complication of breast reconstruction with tissue expanders and silicone implants.