The aim of this prospective study was to determine the effect of screening for methicillin-resistant Staphylococcus aureus (MRSA), in patients undergoing total hip and knee replacements, on reducing hospital-acquired infections and the length of hospital stay. We included 395 patients admitted to the elective orthopaedic ward for hip and knee replacements (knee 210; hip 185) from 16 October 2000 to 15 October 2001. Group 1 included 164 admissions before 16 April 2001 when MRSA swabs were not compulsory. Group 2 included 231 admissions after 16 April 2001 when axillary, nasal and groin swabs had to be negative for MRSA. Four patients in group 1 had post-operative MRSA infection compared with none in group 2. The mean length of hospital stay decreased significantly from 10.43 days +/- SD 4.2 days in group 1 to 9.47 days +/- SD 2.6 days in group 2. There was a significant reduction in the incidence of hospital-acquired infections following the introduction of pre-admission screening.