OBJECTIVES: Benign prostatic hyperplasia (BPH) is a chronic, progressive disease with important healthcare and economic implications. 5-alpha reductase inhibitors (5-ARIs), dutasteride and finasteride are effective treatments. If untreated, BPH may lead to complications such as acute urinary retention (AUR) and the need for surgery (NfS). The aim of this review is to compare the efficacy of dutasteride and finasteride in reducing episodes of AUR and the NfS related to BPH. METHODS: MEDLINE, Lilacs and the Cochrane Central Register of Controlled Trials were searched (from inception to September 2011) to retrieve randomized clinical trials (RCTs) and observational studies evaluating these drugs. The search included articles published in English, Portuguese, and Spanish. Patients with confirmed diagnosis of BPH were included. We analyzed data from studies that reported the number of AUR or NfS following treatment with dutasteride or finasteride. RESULTS: The literature search identified 24 potential full-text publications; 9 RCTs (where 9 were duplicates) and 6 observational/ retrospective studies. No RCT head-to-head comparison was found.  Indirect efficacy comparison between the two 5-ARIs, based on RCTs, was deemed inappropriate due to the heterogeneity of the patients included in the trials, differences in outcome measurements, study design and combination therapies (i.e., alpha blockers) used in the studies. Direct comparison of dutasteride and finasteride was available from 3 retrospective cohort studies, indicating that dutasteride may be more effective in reducing the episodes of AUR (Odds ratio=0.79; 95%CI=0.68-0.93; p=0.0042) and the NfS (Odds ratio=0.77; 95%CI=0.61-0.98; p=0.03) relative to finasteride.  CONCLUSIONS: The current evidence on the efficacy of dutasteride and finasteride makes an indirect comparison between the two 5-ARIs difficult; however, data retrieved from observational studies indicate improved clinical performance of dutasteride compared to finasteride.