Pneumonia is a common infectious disease of the lung, often requiring treatment in the hospital. Clinical scoring systems are available, identifying patients not requiring hospitalization. However, the course of disease of patients in the hospital remains hard to predict. While most patients will recover quickly, some will, despite appropriate treatment, develop a severe course leading to sepsis and systemic responses resulting in organ dysfunction. The PROGRESS study aims to identify clinical, genetic and other molecular markers and combinations thereof predicting a severe course of pneumonia in the hospital. Such predictors will, for instance, support decisions on earlier transfer of patients to intensive care and thus improving outcome.