Following the Chernobyl accident in 1986, sporocarps of Suillus variegatus in Sweden showed a large amount of individual variation in concentration of 137Cs activity. Our aim was to determine the degrees to which this variability in sporocarp 137Cs levels could be explained by differences between (i) local populations, (ii) fungal genets and (iii) locations within genets. Five populations in a 100-yr-old Scots pine forest, located within a 1 km2 area, and two populations in Scots pine/Norway spruce forest, located 40 km north-west of Uppsala, were investigated. In total, 154 sporocarps were analysed to determine their 137Cs content. Of these, the genetic affiliations of 86 were successfully characterized using somatic incompatibility reactions. Twenty-six genets were found which, on average, consisted of 6·5 sporocarps. The genets averaged 7·5 m in size, measured as the length between the most distant sporocarps. The mean sporocarp 137Cs level was 67·1±2·8 kBq kg−1 D.W. (range between 13·6 and 182). According to analyses of variance, within-population variation accounted for 60% of the total variation in 137Cs levels, while 40% was ascribed to variation among populations. Within a population, 137Cs levels did not generally differ significantly between genets. Plausible reasons for intraspecific variation in radiocaesium content in sporocarps are discussed.