BACKGROUND: Unlike influenza, information on the burden of human metapneumovirus (HMPV) as a cause of hospitalizations in adults with acute respiratory illness (ARI) is limited. METHODS: We compared the population-based incidence, seasonality, and clinical characteristics of these 2 viral infections among adults aged ≥20 years with ARI hospitalizations in Auckland, New Zealand, during 2012-2015 through the Southern Hemisphere Influenza Vaccine Effectiveness Research and Surveillance (SHIVERS) project. RESULTS: Of the 14 139 ARI hospitalizations, 276 of 6484 (4.3%) tested positive for HMPV and 1342 of 7027 (19.1%) tested positive for influenza. Crude rates of 9.8 (95% confidence interval [CI], 8.7-11.0) HMPV-associated and 47.6 (95% CI, 45.1-50.1) influenza-associated ARI hospitalizations were estimated for every 100 000 adult residents annually. The highest rates for both viruses were in those aged ≥80 years, of Māori or Pacific ethnicity, or living in low socioeconomic status (SES) areas. HMPV infections were more common than influenza in those with chronic medical conditions. CONCLUSIONS: Although HMPV infections accounted for fewer hospitalizations than influenza in adults aged ≥20 years, HMPV-associated ARI hospitalization rates were higher than influenza in older adults, Māori and Pacific people, and those of low SES. This highlights a need for vaccine/antiviral development.