COVID-19 has had devastating effects on health systems but reports from sub-Saharan Africa are few. We compared inpatient admissions, diagnostic tests performed, clinical characteristics and inpatient mortality before and during the COVID-19 pandemic at an urban tertiary facility in Uganda. We conducted a retrospective chart review of patients admitted at Kiruddu National Referral Hospital in Uganda between January–July 2019 (before the pandemic) and January–July 2020 (during the pandemic). Of 3749 inpatients, 2014 (53.7%) were female, and 1582 (42.2%) had HIV. There was a 6.1% decline in admissions from 1932 in 2019 to 1817 in 2020. There were significantly fewer diagnostic tests performed in 2020 for malaria, tuberculosis, and diabetes. Overall, 649 (17.3%) patients died. Patients admitted during the COVID-19 pandemic (adjusted odds ratio [aOR] 1.2, 95% confidence interval [CI] 1.04–1.5, p = 0.018), patients aged ≥ 60 years (aOR 1.6, 95% CI 1.2–2.1, p = 0.001), HIV co-infected (aOR 1.5, 95% CI 1.2–1.9, p < 0.001), and those admitted as referrals (aOR 1.5, 95% CI 1.2–1.9, p < 0.001) had higher odds of dying. The COVID-19 pandemic disrupted inpatient service utilization and was associated with inpatient mortality. Policy makers need to build resilience in health systems in Africa to cope with future pandemics.