Ambrosia causes most pollen allergies in North America. After several Ambrosia species were introduced to Europe, an increase in the incidence of allergy to pollen of these plants has been observed in many countries. The aim of this study was to compare Ambrosia pollen seasons in 2018 in 13 cities located in different regions of Poland: Bialystok, Bydgoszcz, Cracow, Drawsko Pomorskie, Lublin, Olsztyn, Opole, Piotrkow Trybunalski, Sosnowiec, Szczecin, Warsaw, Wroclaw and Zielona Gora. The study was conducted by the volumetric method using Burkard or Lanzoni pollen samplers. The pollen season was determined by the 98% method. The earliest pollen season start dates (the end of July) were recorded in Zielona Gora, Bydgoszcz, Opole and Szczecin, while the latest ones in Drawsko Pomorskie and Bialystok. The longest pollen seasons occurred in Opole, Szczecin and Zielona Gora (79 days). The highest average daily concentrations of Ambrosia pollen were recorded in Bialystok (129 P/m3) and Lublin (99 P/m3), while the lowest ones in Drawsko Pomorskie and Szczecin (4 and 10 P/m3, respectively). The annual pollen sum reached the highest value in Opole (567 pollen grains) and Zielona Gora (555 pollen grains). It can be concluded from the pattern of Ambrosia pollen seasons at the monitoring sites studied that pollen of this taxon originates not only from Ambrosia locations in Poland but also from long-distance transport.