Background: Viral infections of the respiratory tract in patients with hematological disorders show a similar seasonal pattern to that of the normal population; however, these infections are an important cause of morbidity and mortality in this group of patients. This study evaluated the clinical and laboratory characteristics and outcomes of proven respiratory viral infections (RVIs) and identified risk factors for in-hospital mortality in patients with hematologic malignancies (HM) and hematopoietic stem cell transplant (HSCT) recipients followed at our center. Methods: A single-center, retrospective cohort study comprising patients with HM and HSCT who were diagnosed with RVIs was conducted between January 2023 and June 2025 at a tertiary health center. Patient information was retrospectively collected from the hospital electronic medical records. Baseline mortality predictors were identified using LASSO-penalized logistic regression with 10-fold cross-validation and bootstrap-based selection stability. Clinical deterioration markers were assessed using Firth-penalized logistic regression. Results: A total of 98 patients were included, of whom 19 (19.4%) died in hospital. Serum albumin was the most stable predictor and the only variable retained in the parsimonious model; each 1 g/L increase was associated with lower odds of all-cause in-hospital mortality (OR, 0.82; 95% CI, 0.73–0.91; p < 0.001). The optimism-corrected C-index was 0.828. In univariable analyses, ICU transfer and markers of respiratory deterioration, which reflect the clinical course rather than baseline risk, were associated with higher mortality. Coinfection was also associated with higher mortality (45.5% vs. 16.1%, p = 0.035). Conclusions: In this cohort of patients with HM and HSCT recipients with RVIs, organ dysfunction indicators, clinical worsening, and coinfection were associated with all-cause in-hospital mortality, and lower serum albumin was the most stable independent predictor. These findings highlight the importance of early identification of high-risk patients and close monitoring for respiratory deterioration and coinfections.