BACKGROUND: Infections are the leading cause of death in the first year after heart transplantation (HTx) after the postoperative period. OBJECTIVE: To describe the timing, etiology, and location of the first infection occurring in the first year after HTx. PATIENTS AND METHODS: The study included 604 HTx procedures performed at our center from November 1987 to September 2009. Infections were classified as those requiring hospital admission or that prolonged hospital stay. Infection was established on the basis of clinical findings and supplementary test results. Etiologic diagnosis was established at microbiological culture. Infections were categorized as bacterial, viral, fungal, protozoal, or of unknown origin, and were grouped according to microorganism family. Time to occurrence of infection is given as mean (interquartile range). Locations considered were systemic, pulmonary, genitourinary, cutaneous, oropharyngeal, mediastinal, sternal, gastrointestinal, and other. RESULTS: Mean (SD) patient age was 51 (12) years, and 83.8% of patients were men. Almost half of all patients (42.9%) experienced some type of infection in the first year after HTx. The most frequently occurring infections were bacterial (49.6%) and viral (38.7%), with fewer fungal (6.3%), protozoal (1.2%), and of unknown origin (4.3%). Staphylococci were the most commonly isolated organisms (10.5%) in bacterial infections, cytomegalovirus (21.1%) in viral infections, and Candida (2.3%) and Aspergillus (2.3%) in fungal infections. Early-onset infections (n=2; 1-7 days) were caused by Candida spp, and late-onset infections (n=110; 14-182 days) by a mixed group of bacteria. The sternum was the site of early-onset infections (n=9; 6-14 days), and the genitourinary tract was the site of late-onset infections (n=110; 28-180 days). CONCLUSIONS: Nearly half of HTx recipients experience a significant infection during the first year posttransplantation. Early-onset infections occur in critical care units, are caused by nosocomial organisms, and involve the sternum or mediastinum, whereas late- onset infections have a more varied etiology and preferentially affect the skin and genitourinary tract.