This paper presents a review of the behaviour of radiocesium in plants of forest ecosystems, based on a screening of 375 articles. Particular stress is given to those factors which affect data variability in plants, such as vertical and horizontal patterns of radioactivity in soils due to interception, resuspension, wash-off, litter fall etc. The behaviour of radiocesium in different horizons of forest soils is discussed. The paper summarizes the main uptake mechanisms in fungi, lichens, bryophytes and higher plants, and the possible use of these organisms as bioaccumulators of radioactive deposition. For higher plants, the effects of several factors on root uptake are considered, such as pH, organic matter and clay content of different soil horizons, the concentrations of other ions in the soil solution, rooting depths, mycorrhiza, etc. Finally, the paper includes a discussion of translocation phenomena inside plants, of seasonal variation of radionuclide concentrations, and of the expression of radiocontamination of plant material. The expression of radiocesium concentrations on a water basis is suggested as being more appropriate than the usual expression on a dry weight basis for the solution of several radioecological problems.