[en] After the Chernobyl accident, reindeer pastures in Fennoscandia were contaminated with radioactive material (mainly ¹³⁷Cs). There were large geographical variations in contamination of reindeer and in apparent transfer of ¹³⁷Cs from ground and vegetation to reindeer. There could be several reasons for the observed differences between areas. This work aims at collecting basic data on ¹³⁷Cs activity concentrations in soil, vegetation and reindeer and constructing a model to describe the transfer of radiocaesium to reindeer over time. Field data on ¹³⁷Cs in soil and vegetation has been collected during two years from one reindeer herding district (Jiingevaerie) in central Sweden. Data on ¹³⁷Cs in reindeer is available from the same area from 1986 to 1998. The collected data, and data from earlier investigations, has been put in a simple dynamic model, taking into account ground deposition, initial transfer of ¹³⁷Cs from fallout to different types of vegetation and long term change of ¹³⁷Cs in vegetation as well as food intake, diet composition, absorption and biological half-time of ¹³⁷Cs in reindeer. The ground contamination of ¹³⁷Cs was 9 441 Bq/m², at average, within reindeer pastures used during the summer period and 22 629 Bq/m² within the areas used in wintertime. The relation between ground contamination and vegetation differed very much between sampling sites but were generally higher for lichens (however, not statistically significant) and fungi (significant). The relation between ground contamination and reindeer (T_ag) counted back to 1986 with the observed effective ecological half-time (t_ef = 3. 6 years), was 0. 14 m²/kg for the season August-September and 0. 69 and 0. 66 m²/kg for the seasons October-December and January-April, respectively. Three simulations of ¹³⁷Cs in reindeer over 12 years were made with the constructed model and simulated values were compared to observed activity concentrations of ¹³⁷Cs in reindeer from 1986 to 1998. The simulated curves followed the same pattern as observed values but were slightly high for the summer period. Two simulations (a and c) gave low values for the winter period, while one simulation (b) did not differ significantly from values observed during the winter period. More data need to be collected, especially on relation between ground contamination and contamination of vegetation and long term change of ¹³⁷Cs in vegetation, to get better input data for the model. The variation in diet, and factors that govern changes in diet, also need to be more thoroughly investigated