The ozone concentration ([O-3]), temperature (T) and vapour pressure deficit (VPD) during the 2018 heat wave (HW) was compared with conditions from 2013-2017. The study included one coastal and two inland sites in southwest Sweden. The positive relationship between [O-3] and T was stronger in 2018. The average daytime T from April-September was higher by 2.0-2.4 degrees C in 2018. The VPD was strongly and positively affected by the 2018 HW. The daytime mean [O-3] was enhanced by 7-12% in 2018. The relationship between hourly daytime [O-3] and T, as well as that between the daily maximum [O-3] and daily maximum T, was steeper in 2018. The stronger promotion of [O-3] by T in 2018 was possibly partly a result of dry conditions causing stomatal closure of vegetation and thus a weaker O-3 sink. If HWs like that in 2018 become more common, they can be expected to promote higher [O-3] and risk larger health and ecosystem effects.