The causes of the nineteenth-century decline of mortality, characterized by lower mortality rates and increased longevity, have been the subject of debate among researchers for the past half-century. Because of a paucity of reliable data, little is understood about the role of morbidity, or illness episodes, in the mortality decline. This article introduces the results of a study that looks at the relationship of morbidity in the mortality decline during this portion of the epidemiological transition. The data are comprised of hospital admissions and deaths collected by the British army on the soldiers of the Gibraltar garrison from 1819 to 1899. Morbidity dropped during this period, but at a slower rate than mortality, and all categories of disease did not fall in concert; in some categories, morbidity rose as mortality dropped. Statistical modeling is used to analyze the categories of diseases that were most influential in the decline of mortality in this group. This research shows that there are discernible relationships between morbidity and mortality and that the two parameters are responding to different driving forces. Because changes within the military medical system may have had an effect on the relationship of the morbidity and mortality rates of the soldiers, surviving medical reports are used to reconstruct the medical care of the troops during the study period.