This paper reports on results of activity mass concentration analyses performed in various forest mushrooms in the Czech Republic within 1986 and 2011. The estimated effective half-life of ¹³⁷Cs and its environmental half-life (i.e. the effective half-life minus the effect of physical decay) were found to be 5.6±0.6 and 6.9±0.7 y, respectively. Non-homogeneity in ¹³⁷Cs surface contamination over the country's territory and fungus species-based ¹³⁷Cs accumulation capacity then account for a span of up to 4 orders of magnitude in activity mass concentrations measured each year after the Chernobyl accident. The highest geometric activity mass concentration (Bq kg⁻¹ of dry weight) means of ¹³⁷Cs (obtained from samples between years 2004 and 2011) were measured in Suillaceae (1050 Bq kg⁻¹) and Boletus badius (930 Bq kg⁻¹), the lowest in Agaricus (1 Bq kg⁻¹). The geometric mean of all mushrooms amounted to 230 Bq kg⁻¹, being 440 Bq kg⁻¹ in Boletales, 150 Bq kg⁻¹ in Russulales and 21 Bq kg⁻¹ in Agaricales. Geometric standard deviation levels were generally high. The highest Cs accumulation capacity was observed in Boletales (namely in Suillaceae), while the lowest in Agaricales, being over 3 orders of magnitude lower than in Suillaceae.