Small- and medium-sized companies obtain ISO 9000 quality management systems as a way of adapting to the changes of business environment and improving their business performance. Certificates of ISO 9000 quality management systems have been granted to companies by either domestic or foreign certification agencies with different requirements and standards. This study empirically examined whether there are differences in business performance among small- and medium-sized companies that have obtained ISO 9000 quality management system from different types (domestic or foreign) of certification agencies. This study found that there are statistically significant differences in both qualitative and quantitative business performance among them. The findings of this study imply that companies considering ISO 9000 quality management systems be prudent in choosing the type of certification agency to maximize the expected benefits of ISO 9000 quality management systems. This study also provides the government agency regulating ISO 9000 quality management certification system with some valuable information that brings up the need for establishing and managing a more effective quality management certification system.