OBJECTIVE To determine the spread of respiratory infection with Mycoplasma pneumoniae in an institute for mentally disabled persons. METHODS Descriptive. METHODS In the period from mid-April to mid-September in a certain year the transmission of M. pneumoniae in the facility was evaluated using questionnaires and laboratory investigations. The laboratory investigations consisted of an M. pneumoniae specific polymerase chain reaction (PCR) on throat swab specimens and detection of antibodies in serum. RESULTS 21 Residents and 26 staff members from 2/36 units were involved in the initial investigation. 17 Persons had complaints of a (recent) respiratory infection (cough, malaise and fever). In 9 cases an M. pneumoniae infection was confirmed, in 5 cases by PCR and in 4 cases by serology. Two PCR positive persons had only complaints of coughing. During the investigation period 2 more persons were diagnosed with a respiratory infection due to M. pneumoniae. No new cases were found by investigation of contacts outside the facility. CONCLUSIONS M. pneumoniae can cause an outbreak of M. pneumoniae respiratory infection in an institute for mentally disabled persons. Rapid detection of this pathogen is possible by PCR and is important for proper antibiotic therapy and epidemic-control measures.