The 10 most common diseases in the world are: heart disease, stroke, chronic respiratory disease, chronic obstructive pulmonary disease, lower respiratory infections, diabetes, HIV/AIDS, malaria, tuberculosis, and cancer. All of these diseases are preventable, and can be treated with proper medical care. Heart disease is the leading cause of death in the world, followed by stroke, chronic respiratory disease, and chronic obstructive pulmonary disease. Lower respiratory infections, diabetes, HIV/AIDS, malaria, tuberculosis, and cancer are all leading causes of death as well. All of these diseases can be prevented or treated through proper medical care, lifestyle changes, and vaccinations.