The clinical relevance of second-line drug susceptibility test (DST) results with respect to treatment outcome is unknown in non-XDR MDR patients. This study was carried out in the sole national referral centre for TB in Iran between 2002 and 2006. Multidrug-resistant tuberculosis (MDR-TB) patients who had DST to second-line drugs were included. For all MDR-TB patients the standard second-line regimen was initiated. Outcome of treatment based on DST to second-line drugs was analysed. 53 patients were included. DST for second-line drugs was available for 40 patients. Seven patients returned to Afghanistan during treatment. Among the remainder, 13 (30.4%) cases were Iranian. Mean age was 40.8 + 19.7 y. The relatively small sample size imposes some limitations on this study. However, in this study, there was no difference in resistance to second-line drugs by nationality. No significant correlation was seen between resistance to second-line drugs and outcome of treatment. In conclusion, the treatment outcome according to WHO definitions was appropriate in the study population by the use of standardized treatment regimens. Follow-up studies on a long-term basis are however needed in order to detect possible relapses.