BACKGROUND: Preliminary reports described a reduction in non-COVID admissions during the first wave of the pandemic including some of critical diseases such as cancer, myocardial and cerebral infarction. OBJECTIVE: The aim of our study was to evaluate the impact of the COVID-19 pandemic on non-COVID in-hospital admissions in a large academic center in Belgium. MATERIALS AND METHODS: We performed a retrospective study of non-COVID-19 in-hospital admissions during the first two waves of the COVID-19 pandemic. The average number of admissions per week in 2020 has been compared to that of the same period in 2019 and 2018. Comparisons were made first for all admissions, then by disease groups, using the classification of APRDRG, and then by diagnoses using ICD-10-CM classification. RESULTS: Overall in-hospital admissions were reduced by around 39% and 29% during the first and the second waves of the COVID-19 pandemic respectively compared to 2018 and 2019. No significant difference was found between the average number of admissions in the early-COVID and the pre-COVID baseline period during the two waves. The average number of admissions was significantly reduced in the peak-COVID period compared to the baseline (first wave: 332 versus 763 admissions/week, p<0.01, -57%; second wave: 496 versus 788 admissions/week, p<0.01, -37%), as well as in the late-COVID period compared to the baseline (first wave: 412 versus 763 admissions/week, p<0.01, -46%; second wave: 470 versus 788 admissions/week, p<0.01, -40%). Cancer, myocardial and cerebral infarction admissions were not statistically reduced during the the two waves of COVID pandemic compared to the pre-COVID period. CONCLUSION: Our study shows that non-COVID in-hospital admissions rates were substantially reduced during the first two waves of COVID-19 pandemic. In our study, cancer, myocardial and cerebral infarction admissions were not statistically reduced, which was not in accordance to what was described in the literature.