An analysis of 143 firms in the Greek manufacturing and service sectors reveals that adopters of ISO 9000 quality assurance schemes are larger companies producing intermediate goods, but less profitable and with higher leverage than their non-adopter counterparts. The effects of adopting an ISO 9000 scheme on firm performance and especially on certain dimensions of profitability are not significant in a period of 5-6 years after adoption. Evidence suggests that the adoption of an ISO 9000 quality assurance scheme, being a continuous process of improvement, is beneficial in the long term and does not necessarily improve financial ratios in the short term. Active support policies for the promotion and dissemination of quality standards in the manufacturing and service sectors of Greece can be reconsidered and a more targeted policy should be implemented. Future research may be designed and implemented so that long-term and strategic effects of the adoption of the new ISO 9000: 2000 standards are revealed.