Many medical procedures breach or suppress patients’ natural defences, leaving them vulnerable to infections which would not occur in healthy humans: “healthcare-associated infections”. Healthcare-associated infections caused by the bacterium Staphylococcus aureus (S. aureus) are probably the most feared, due to the invasive nature and the wide occurance of the pathogen. This thesis explored risk factors, diagnostic procedures, outcome and treatment options of a number of healthcare-associated infections caused by S. aureus, with a focus on bacteriuria, neurosurgical infections and intravascular catheter-associated infections. Eligible patients for the studies were identified through searches in microbiology laboratory management and information systems. The wide range of infections which S. aureus may cause, made the research questions and outcomes of the thesis quite diverse: 1. A relation between S. aureus bacteriuria (bacteria in the urine) and S. aureus bacteremia (bacteria in the bloodstream) has been described in the past. It was believed that bacteria reached the urine from the bloodstream. In our studies we found no evidence for this phenomenon. In fact, the opposite appears to be the case: S. aureus often invades the bloodstream from the urinary tract, and bacteriuria is risk factor for subsequent bacteremia. 2. The most frequently performed procedure in neurosurgery is the placement of cerebrospinal fluid drains, devices intended to lower intracranial pressure. Our studies found that when these drains are colonized with bacteria, the chance of developing meningitis is approximately fifty-two percent. This chance increases to over seventy percent when the colonizing micro-organism is S. aureus. Furthermore, cases of meningitis in neurosurgical patients experienced at the UMC Utrecht were evaluated to sharpen the diagnostic criteria for this complication. 3. Intravascular catheter-associated infections with S. aureus were investigated. Intravascular catheters, or “central lines”, are plastic tubes inserted in a major vein or artery, to administer medication, fluids and blood products, or to monitor blood pressure. Two studies within this thesis found that colonization of these catheters with S. aureus was such a strong risk factor for subsequent bacteremia, that prophylactic therapy was needed. To prevent one case of bacteremia, only eight patients required antibiotic treatment. Also, we studied patients with catheter-associated S. aureus bacteremia to quantify how the speed of medical interventions affects the survival of these patients. The two main actions a physician takes in these patients is to start antibiotic treatment and to remove the infected catheter. It was found that the relation between rapid therapeutic actions and outcome is so complex in this patient group, that all research performed thus far is inadequate to answer this question. 4. The heavy use of antibiotics in healthcare has rendered a large proportion of pathogenic micro-organisms resistant against many antimicrobial agents. New antibiotics are needed. To conclude this thesis, we describe how epilancin 15X, a novel antibiotic compound with activity against important healthcare-associated pathogens, was isolated from a strain of Staphylococcus epidermidis. Although epilancin 15X will not be directly usable to treat patients, the elucidation of its structure may lead to the development of actual antibiotics in the future.