SETTING: The detection of multidrug-resistant tuberculosis (MDR-TB) using rapid drug susceptibility testing (DST) has increased steadily in recent years in Peru, from 9216 tests in 2010 to 27 021 tests in 2015. Research examining the impact of rapid DST on treatment outcomes is required. OBJECTIVE: To evaluate the association between rapid DST use (nitrate reductase assay, microscopic observation drug susceptibility assay [MODS] and GenoTypew MTBDRplus) and treatment outcomes and mortality in MDR-TB patients in Peru. DESIGN: Retrospective cohort study of patients diagnosed with pulmonary MDR-TB between 2010 and 2013 (with treatment outcomes up to December 2015) using the electronic registry of the Peruvian National TB Programme. RESULTS: A total of 2671 MDR-TB patients were included; the median age was 27 years, 2.8% were co-infected with the human immunodeficiency virus. Use of rapid DST was associated with a 40% increase in the adjusted odds of treatment success (aOR 1.40, 95%CI 1.19-1.64) and a 54% reduction in mortality (aOR 0.46, 95%CI 0.33-0.64). Higher treatment success rates were driven by MODS and GenoTypew MTBDRplus testing (aORs for unsuccessful outcomes respectively 0.68 and 0.66). CONCLUSION: The use of rapid DST (MODS and MTBDRplus) to diagnose MDR-TB was associated with a reduction in the odds of death and a substantial increase in the odds of treatment success.