High stomatal ozone (O 3 ) uptake has been shown to negatively affect crop yields and the growth of tree seedlings. However, little is known about the effect of O 3 on the carbon uptake by mature forest trees. This study investigated the effect of high O 3 events on gross primary productivity (GPP) for a Scots pine stand near Antwerp, Belgium over the period 1998–2013. Stomatal O 3 fluxes were modelled using in situ O 3 mixing ratio measurements and a multiplicative stomatal model, which was parameterised and validated for this Scots pine stand. Ozone-induced GPP reduction is most likely to occur during or shortly after days with high stomatal O 3 uptake. Therefore, a GPP model within an artificial neural network was parameterised for days with low stomatal O 3 uptake rates and used to simulate GPP during periods of high stomatal O 3 uptake. Possible negative effects of high stomatal O 3 uptake on GPP would then result in an overestimation of GPP by the model during or after high stomatal O 3 uptake events. The O 3 effects on GPP were linked to AOT40 and POD 1 . Although the critical levels for both indices were exceeded in every single year, no significant negative effects of O 3 on GPP were found, and no correlations between GPP residuals and AOT40 and POD 1 were found. Overall, we conclude that no O 3 effects were detected on the carbon uptake by this Scots pine stand.