The Coronavirus Disease 2019 (COVID-19) pandemic posed various challenges to the healthcare system and disease management. This study aimed to describe changes in the clinical characteristics and outcomes of hospitalized patients during the first year of the COVID-19 pandemic in a city in southern Brazil. This prospective study was carried out in two tertiary care private hospitals in Curitiba. A total of 1151 patients hospitalized between March 2020 and March 2021 were included. We identified three epidemiological critical periods of the pandemic and compared patients’ characteristics and the frequencies of oral intubation, intensive care unit (ICU) admission and mortality. Continuous variables were analyzed by variance analysis model (ANOVA) or the Kruskal–Wallis nonparametric test and categorical variables by the chi-square or Fisher’s exact test. Models for univariate and multivariate logistic regression analysis were adjusted to identify the factors associated with mortality. All p-values were two-tailed and p<0.05 was considered statistically significant. The average age of the patients was 58 years and 60.9% (n = 701) were males. The most prevalent comorbidities were systemic arterial hypertension, diabetes and obesity. There were no significant variations in the demographic characteristics and previous comorbidities of the patients for the different periods of analysis. Mortality was positively associated with the age ≥65 years and the presence of one or more cardiometabolic comorbidities (p<0.001). March 2021 was the most important critical period of the pandemic since there were higher frequencies of patients admitted later in the course of the disease, with desaturation and more symptoms at hospital admission (p<0.001). There was also an increase in the duration of hospital stay (p<0.001) and the frequencies of all critical outcomes for this period: oral intubation (p<0.001), ICU admission (p = 0.606) and mortality (p = 0.001). Our key findings revealed that, although there were no statistically significant differences between the subgroups of hospitalized patients over time in terms of demographic characteristics and comorbidities, the course of COVID-19 was significantly more severe for patients admitted to the hospital at the end of the first year of the pandemic in Brazil.