This paper explores how changes in macroeconomic uncertainty have affected the decision to participate in the European Central Bank's Survey of Professional Forecasters. Two different approaches are employed in order to address this question. First, a time-series analysis explores if changes in measures of uncertainty over time have led to changes in aggregate response rates. And second, a discrete-choice model for panel data is estimated to test if changes in uncertainty measures have had effects on the likelihood to participate by SPF forecasters. The main result of the paper is that higher (lower) uncertainty reduces (increases) participation in the survey. This effect is statistically and economically significant. As participation and uncertainty are found to be negatively correlated, measures of uncertainty from the ECB's SPF could be biased downwards.