Purpose Chronic tendinopathy of lateral epicondyle of the humerus, commonly known as Btennis elbow^is one of the most frequent tendinopathies caused by recurrent overload of the muscle origins. The aim of the study was to assess the effectiveness of treating lateral epicondylitis (LE) with autologous conditioned plasma (ACP) and betamethasone injections, and to compare these methods over the course of a one year follow-up. Methods Patients were randomly placed into one of into two groups: 53 were treated with ACP, and 46 with 1 ml betamethasone injections and 2 ml of 1 % lignocaine. Both those groups were comparable in terms of initial DASH score. Results After six weeks and six months, the mean DASH score was significantly better in the betamethasone group, but was better in ACP group after one year. Full recovery (patients with no symptoms) at all time points was more common in the betamethasone group. A comparison of grouped DASH scores revealed more very good and good results in the ACP group after one year. More patients had pain symptoms related to injection in the ACP group than the betamethasone group. Conclusions ACP therapy of LE allows better results to be obtained at 12 months. Betamethasone injections give more rapid improvement, but the therapeutic effect is longer lasting in the ACP group.