Background. Influenza A(H5N1) continues to cause infections and possesses pandemic potential. Methods. Data sources were primarily clinical records, published case series, and governmental agency reports. Cox proportional hazards regression was used to estimate the effect of treatment on survival, with adjustment using propensity scores (a composite measure of baseline variables predicting use of treatment). Results. In total, 308 cases were identified from 12 countries: 41 from Azerbaijan, Hong Kong SAR, Nigeria, Pakistan, and Turkey (from clinical records); 175 from Egypt and Indonesia (from various sources); and 92 from Bangladesh, Cambodia, China, Thailand, and Vietnam (from various publications). Overall crude survival was 43.5%; 60% of patients who received ≥1 dose of oseltamivir alone (OS+) survived versus 24% of patients who had no evidence of anti-influenza antiviral treatment (OS-) (P < .001). Survival rates of OS+ groups were significantly higher than those of OS- groups; benefit persisted with oseltamivir treatment initiation ≤6-8 days after symptom onset. Multivariate modeling showed 49% mortality reduction from oseltamivir treatment. Conclusions. H5N1 causes high mortality, especially when untreated. Oseltamivir significantly reduces mortality when started up to 6-8 days after symptom onset and appears to benefit all age groups. Prompt diagnosis and early therapeutic intervention should be considered for H5N1 disease.