Aim of the study: Evaluation of safety and therapeutic effectiveness of leflunomide according to age of the patients and duration of rheumatoid arthritis. Methods: Leflunomide therapy safety was analyzed in a group of 261 patients based on number of adverse effects responsible for treatment interruption and according to adverse effects number that allowed for continuing therapy. During six-month observation 27 patients interrupted therapy and in the group of remaining 234 persons leflunomide therapy efficacy was evaluated according to DAS-28 score. Results: Efficacy of leflunomide therapy was confirmed in every group according to patients age and no significant differences were observed between groups of patients with different age. Adverse leflunomide effects occurred in 47 (18.8%) patients and were the cause of therapy interruption in 23 (8.8%) cases. No significant differences in adverse leflunomide effects were observed to depend on patients age or rheumatoid arthritis period. Conclusions: (1) Patients’ age and period of rheumatoid arthritis do not influence leflunomide therapy safety. (2) Efficacy of leflunomide was confirmed in each group of patients. (3) Patients’ age does not influence leflunomide therapy outcome.