Increasing dissemination of Methicillin-resistant S. aureus (MRSA) calls for a more consequent examination of the causal mechanisms. Experiences and results of analysis of three different outbreaks caused by MRSA are described. In summary it is shown that MRSA are especially epidemic virulent and persist over a long range of time in a care unit. Main reasons for these outbreaks obviously were mistakes in hospital hygiene and an inappropriate antibiotic prophylaxis. Predisposed inpatients suffer from severe infections. Interregional dissemination of MRSA observed is mainly due to the transfer of patients between hospitals. Optimization of hospital hygiene especially isolated or cohort nursing of affected patients as well as restriction of antibiotic prophylaxis and therapy are crucial measures against the dissemination of MRSA. For success of these measures information and motivation of staff are necessary.