Major problems with excessive growth, reduced light conditions, poor flower bud development and low yields have developed in many orchards with the sour cherry 'Stevnsbaer'. To investigate the possibility of handling the problems by root pruning, a project was initiated in 2003. Three orchards with trees of middle age on rootstock Colt were selected. Three trees with intact root systems were pulled up in each of the orchards. Based on the architecture of the root systems, a pruning distance of 30-35 cm from the trunk was used, removing approximately 30 percent of the roots. The one-sided root pruning was carried out either in April or in June with a curved knife reaching a depth of 75 cm and with a bend of 25 cm in the lower 30 cm. One hundred and eighty, 2-year-old branch systems were labelled and shoot number, shoot length, bud number (April), flowers, pistil damaged or late opening flowers (May), initial and final fruit set (June) were recorded. Root pruning had little effect on fruit set, fruit size and yield in the year of pruning. Only in one plot with a severe root pruning (26 cm from the trunks), negative effects were found. The effects on growth, flowering and fruit set in 2003 and 2004 are reported and the prospects for improved growth control in sour cherry by root pruning are discussed.