Purpose – There has been little evidence of any work undertaken to measure the effectiveness of viral marketing campaigns. This paper aims to report on research undertaken to determine the key criteria that viral marketing practitioners believe should be used to measure the success of viral marketing campaigns.Design/methodology/approach – Semi-structured interviews were undertaken with some of the premier web masters, those leading the development of much of the UK’s viral marketing activities. Findings – Two forms of viral marketing were identified, “random” and “placed virals”. The paper presents a viral marketing evaluation framework that identifies three key objectives and their particular evaluation criteria. Financial objectives and the need to measure the return on investment were identified as previously undocumented key issues. Research limitations/implications – The small size of the sample prevents generalization but the findings suggest that further research is necessary to confirm these findings and to explore the topic in greater detail. Practical implications – Using the framework to measure the success of a campaign can help clients and agencies be more accountable and effective with respect to viral campaigns. Originality/value – The determination of the evaluation of critieria of viral marketing campaigns is important because it is undertaken from a practitioners’ perspective and is a topic not previously explored.