The aim of the present study was to compare the mugwort pollen season in 2018 in Bialystok, Bydgoszcz, Cracow, Drawsko-Pomorskie, Lublin, Olsztyn, Opole, Sosnowiec, Szczecin, Warsaw, Wroclaw, and Zielona Gora. Pollen concentration measurements were made by the volumetric method using Burkard or Lanzoni pollen samplers. The pollen season was considered as the period during which 98% of the total annual pollen count occurred. The Seasonal Pollen Index (SPI) was calculated as the sum of the average daily pollen concentrations throughout the season determined for the individual cities. The mugwort pollen season started earliest in Bialystok (June 21st) and Bydgoszcz (June 25th), while in the other cities its onset occurred in the first 10 days of July. Significant differences were found in season duration (68–110 days), SPI, and peak value. The longest season occurred in Zielona Gora and Bydgoszcz, while the shortest one in Wroclaw. The highest SPI and maximum concentration values were observed in Lublin and Zielona Gora. In most of the cities, the peak value was recorded in the first 10 days of August. The highest risk of allergy in people sensitive to the pollen of this taxon was found in Zielona Gora, Lublin, and Warsaw.