The limited experience in treating patients with extensively drug-resistant tuberculosis (XDR-TB) shows a therapeutic success rate under 50-60% and there are no publications regarding the outcome of these patients treated with standardized regimens. All multidrug-resistant tuberculosis (MDR-TB) patients hospitalized at the Masih Daneshvari Hospital in Tehran, Iran, during 2004-2007 were recruited. Drug susceptibility testing to 14 drugs (including eight second-line drugs) was performed and a standardized regimen with ofloxacin, cycloserine, prothionamide, and amikacin was administered for all patients. Outcome of the patients was studied, comparing between the MDR-TB non-XDR-TB and the XDR-TB. Fifty-one patients were included, 12 with XDR-TB criteria. Of 51, 48 were HIV negative and HIV status was unknown in three cases. All 12 were HIV negative. XDR-TB infection was significantly associated only with age (p = 0.039). The success rates for the total 51 MDR-TB, the 39 MDR-TB non-XDR-TB, and the 12 XDR-TB patients were 76.5% (39 patients), 87.2% (34 patients), and 41.7% (5 patients), respectively. Resistance to ofloxacin, ciprofloxacin, and amikacin were found to be significantly associated with unsuccessful outcome. In this setting, a standardized second-line drugs regimen produces high treatment success rates in MDR-TB patients unless XDR-TB is present.