In spite of the conspicuous use of the Internet as a delivery channel, there is a relative dearth of empirical studies that provide a quantitative analysis of the impact of the Internet on banks´ financial performance. This paper attempts to fill this gap by identifying and estimating the impact of the adoption of a transactional web site on financial performance using a sample of 72 commercial banks operating in Spain over the period 1994-2002. The impact on banks´ performance of transactional web adoption takes time to appear. The adoption of the Internet as a delivery channel involves a gradual reduction in overhead expenses (particularly, staff, marketing and IT). This effect is statistically significant after one and a half years after adoption. The cost reduction translates into an improvement in banks´ profitability, which becomes significant after one and a half years in terms of ROA and after three years in terms of ROE. The paper also concludes that the Internet is being used as a complement to, rather than a substitute for, physical branches.