In the aftermath of the Chernobyl accident high concentrations of ¹³⁷ Cs were found in mushrooms in several European countries and inSweden. Two edible mushrooms species were selected for a long-term investigationin order to evaluate the ¹³⁷Cs contamination over a long time.Samples of Suillus variegatus and Cantharellus spp. were collected from 1986to 1998 and their ¹³⁷ Cs contents assessed. The results show thatthe activity of ¹³⁷Cs remained more or less constant in Suillusvariegatus, while it increased in Cantharellus spp. This reflects the forestecosystem of the mushrooms, where nutrient-poor substrates, rich in organicsubstance and with high pH maintain ¹³⁷Cs available for uptake.A decay-correction of the time distribution shows that radioactive decay appearsto be the main factor affecting the content of ¹³⁷Cs in mushrooms,at least in the medium term.