This paper investigates whether engagement in consulting activities has a significant impact on the research performance of academic scientists. The study relies on a sample of 2678  individual faculty, from five Spanish universities, who have been recipients of publicly funded grants or have been principal investigators in activities contracted by external agents over the period 1999-2004. By implementing a propensity score matching estimator method, we show that engaging in consulting activities has an overall negative impact on the average  number of ISI-publications. However, the effect of consulting on the scientific productivity of academic scientists depends on the scientific fields and the intensity of engagement in  consulting activities. Academic consulting is found to have a negative impact in the fields of ‘Natural and Exact Sciences’ and ‘Engineering’, but not in the case of ‘Social Sciences and Humanities’. When the intensity of consulting activity is taken into account at the discipline level, engaging in consulting activities has an overall negative impact on scientific productivity only for high levels of involvement in consulting activities, but not for moderate ones.