Background: Gastric cancer remains a major contributor to cancer-related morbidity and mortality worldwide, disproportionately affecting middle- and low-income settings. In Brazil, rapid population aging, persistent exposure to risk factors, and structural inequalities in access to early diagnosis place substantial pressure on hospital services. The coexistence of the public Unified Health System (SUS) and the supplementary private health sector offers a unique opportunity to examine how different financing and care models shape hospitalization patterns for gastric cancer. Objectives: To characterize and compare hospitalization rates, demographic profiles, temporal trends, and mean length of hospital stay for gastric cancer in the public (SUS) and supplementary health systems in Brazil’s Central-West region between 2015 and 2024. Methods: An ecological study was conducted using secondary, aggregated data on hospitalizations with a primary diagnosis of gastric cancer (ICD-10 C16). Data for the SUS were obtained from the Oswaldo Cruz Foundation’s Observatory of Hospital Policy and Management, and supplementary sector data from the National Agency for Supplementary Health. Population estimates by age and sex from the Brazilian Institute of Geography and Statistics were used to calculate hospitalization rates per 100,000 inhabitants, which were age-standardized using the World Health Organization standard population. Descriptive analyses were performed by sex and age group. Temporal trends were assessed using Joinpoint regression to estimate annual percentage changes and identify statistically significant inflection points. Results: Between 2015 and 2024, 19,166 hospitalizations for gastric cancer were recorded in the SUS, with a statistically significant upward trend throughout the period. Hospitalization rates were consistently higher among men; however, women experienced a steeper relative increase over time. Age-stratified and age-standardized analyses showed a pronounced concentration of hospitalizations among individuals aged ≥60 years, who exhibited the highest rates and the strongest temporal growth, as confirmed by Joinpoint regression. In contrast, hospitalization rates among younger age groups (20–39 and 40–59 years) remained low and stable.  In the supplementary health sector, hospitalization rates were substantially lower than in the SUS, predominantly affected men, and showed no statistically significant temporal trends across sex or age strata. Mean length of hospital stay declined progressively in the SUS for both sexes, suggesting improvements in hospital efficiency and care organization, although older adults consistently experienced longer stays. In the supplementary sector, mean length of stay was shorter overall but demonstrated greater year-to-year variability, particularly among men, likely reflecting smaller case volumes and heterogeneous clinical profiles. Conclusions/Implications: Hospitalizations for gastric cancer are increasing significantly in Brazil’s public health system, underscoring the SUS as the primary provider of complex oncological care, especially for older and more vulnerable populations. The contrasting stability observed in the supplementary sector highlights persistent structural inequalities in access to early diagnosis and outpatient management. Despite growing demand, reductions in length of stay suggest gains in SUS performance. Strengthening early detection, expanding diagnostic capacity, and reinforcing integrated care networks within the SUS are essential to mitigate avoidable hospitalizations and ensure equitable gastric cancer care in aging populations.