Methodologies and procedures for environmental hygiene surveillance of operating room theatres are not uniform across Italy. The aim of this study was to implement a surveillance model based on total mesophilic load and particle count, and evaluating the model's efficacy and sensitivity. The surveillance model was introduced in 2008 for the evaluation of hygienic-sanitary conditions of seven operating theatres in two hospitals in Rome (Italy). In total 924 samples were tested. The correlation between total mesophilic load and particle count seem to indicate the efficacy of this model, although the two indicators appear to be complementary and cannot substitute one another.