Ragweed poses a health and an agricultural risk that need to be assessed in Latvia by determining the growth of ragweed plants and pollen transported from local sources and neighboring countries. It has been stated that the northern border for the growth of ragweed exists at the 55o latitude north and Latvia is situated between the 55 and 58° latitude north. This study investigates the collection of ragweed plants during field studies of other plants (1970- 2007) and pollen collected from aerobiological monitoring in Riga starting from 2003. Ragweed is classified as an invasive plant species and was found growing alongside main transportation routes (railways and roads) in Latvia. The most harmful species, A. artemisiifolia, represented 84% of all the ragweed plants, followed by 9% of A. trifida and 5% of A. psilostachya. Field studies in 2007 that located ragweed were repeated, but no plants were found in the same locations in 2011. Herbariums have revealed that ragweed plants have flowered between the middle of July until September. Aerobiological studies have revealed ragweed pollen during the day within a two weeks period between late August and the start of September that suggests pollen from local sources. The pollen concentration only reached a concentration of 2-3 grains/m3 over the two weeks period starting in August. Ragweed pollen is presently not a threat in Latvia, but more studies need to be conducted to follow any changes over time.