The purpose of this paper is to dissect the diffusion of the number of organizations that implemented multiple management systems (MSs), considering the International Organization for Standardization (ISO) 9001, ISO 14001 and OHSAS 18001 standards (quality, environment and safety) in the South European countries: Italy, Portugal and Spain. In addition, based on the data collected, forecasting models were developed to assess at which extent the multiple certifications are expected to occur in each studied country.