BACKGROUND: Clinical reports have raised concern about local complications following breast implantation used in reconstructive or cosmetic surgery, but there is a shortage of epidemiological studies in this area. OBJECTIVE: To assess in a prospective epidemiological manner the occurrence of short-term local complications in a nationwide implantation registry. DESIGN, SETTING, AND PARTICIPANTS: The Danish Registry for Plastic Surgery of the Breast prospectively collects preoperative, perioperative, and postoperative information on Danish women undergoing breast augmentation. Through the registry, we collected data on short-term local complications among 574 women who underwent postmastectomy reconstruction with breast implants from June 1, 1999, through July 24, 2003. MAIN OUTCOME MEASURES: Complication incidence rates. RESULTS: Thirty-one percent of the women who underwent initial implantation developed at least 1 adverse event. Forty-nine percent of the adverse events occurred within 3 months after implantation and 67% within 6 months. Surgical intervention was required after initial implantation among 21% of women, most frequently because of capsular contracture, asymmetry, or displacement of the implant. Thirty-six percent of women who underwent subsequent implantation experienced at least 1 adverse event, and 21% underwent surgical intervention to treat definitive complications or to optimize cosmetic result. CONCLUSIONS: Women who undergo postmastectomy breast implantation frequently experience short-term local complications. Surgical or medical intervention is commonly required during the reconstructive course, but reconstruction failure (loss of implant) is rare. However, when weighing benefits and risks associated with reconstruction, the patient should consider that breast reconstruction is a process involving planned and unplanned supplementary surgical correction to achieve the desired result.