Background Enterococcus faecium has rapidly emerged as a nosocomial pathogen worldwide, and the majority of these isolates belong to clonal complex-17 (CC17). In Europe, CC17 isolates are usually ampicillin-resistant, but most are still vancomycin-sensitive. We aimed to study ampicillin-resistant E . faecium (ARE) epidemiology in our hospital. Methods In a 3 month study, 210 of 358 admissions (59%) to haematology and gastroenterology/nephrology were screened for rectal ARE colonization on admission (<48 h) and 148 of 210 (70%) also at discharge (<72 h). In a second (3 month) study, environmental swabs from eight predetermined sites were obtained from ARE-colonized haematology patients once weekly. All ARE isolates were genotyped by multiple-locus variable-number tandem repeat analysis (MLVA). Results ARE admission prevalence was 10% and 16% and acquisition rates were 39% and 15% in haematology and gastroenterology/nephrology, respectively. Carriage on admission was associated with previous admission <1 year (OR 5.0, 95% CI 1.8–14.0) and acquisition with β-lactam (OR 2.7, 95% CI 1.1–6.7) and quinolone use (OR 3.1, 95% CI 1.1–8.2). Five of the 57 (9%) colonized patients developed invasive ARE infections. Genotyping revealed 12 genotypes (all CC17) with two MLVA types responsible for 94% of acquisitions. In 18 of the 19 colonized patients, the environment was contaminated with ARE. Sites most often contaminated were the toilet seat (43%), over-bed table (34%) and television remote control (28%). Conclusions CC17 ARE epidemiology is characterized by high admission (10% to 16%), acquisition (15% to 39%) and environmental contamination (22%) rates, resulting from cross-transmission, readmission and antibiotic pressure. A multifaceted infection control approach will be needed to curtail further spread.