Background: Treatment failure and relapse is a major problem in the treatment and control of brucellosis. The present study directed to determine risk factors for failure of treatment and relapse in patients treated for brucellosis.

Materials and Methods: This study was a descriptive - analytic and prospective study and were conducted in 72 patients with acute brucellosis.Patients were followed up during treatment and for six months after completion of therapy, and patients with treatment failure or relapse were analyzed. All data analyzed using SPSS software and P-value of less than 0.05 was considered significant.

Results: The mean value of age in patients was 40.2 ± 16.5 years. Treatment failures was 6.9% and the relapse at the end of the ninth month was 12.5% that recurrence of symptoms were associated with increased titers of serological tests and 80.6 percent had successful treatment. In this study gender of male (P = 0.026), occupational exposure (P = 0.005), delayed treatment in less than two weeks (P = 0.016), hepatosplenomegaly (P = 0.003), thrombocytopenia (P = 0.023), CRP &ge +2 (P = 0.017) and Wright &ge 1/320 and 2-ME &ge 1.160 at the end of the sixth week of treatment (P = 0.004 and P = 0.010) were risk factors of treatment failure and relapse in brucellosis.

Conclusion: The diagnosis and treatment of relapse and treatment failure in acute brucellosis is not clear, therefore, the prediction of relapse may be useful in preventing recurrence and treatment of patients.