Brooklyn Diet Dispensary.

In colonial New York, only a small number of almshouse infirmaries existed to care for the sick, while the mentally ill were usually imprisoned or placed in poorhouses. It was not until the early to mid-19th century, when the New York City area's dependent and poor population increased dramatically, that hospitals and other health services organizations, such as homeopaths and maternity wards, readily began to emerge. In Brooklyn specifically, the earliest hospitals included the Kings County Hospital, which grew out of an almshouse infirmary in 1831, and the Brooklyn City Hospital, which was incorporated in 1845. One of Brooklyn's first mental institutions was also established in Flatbush in 1845.

Most health services organizations that were established during this period were affiliated with charitable organizations, religious denominations, or ethnic groups, and had meager resources with which to care for patients. Hospitals, for instance, provided shelter, meals, and only minimal medical care, usually administered by poorly trained staff in unsanitary conditions, while mental health institutions suffered from extreme overcrowding. Because of the social stigma attached to such institutions, middle and upper class citizens usually received medical care in the privacy of their homes.

Popular attitudes toward public health institutions began to change in the late 19th and early 20th centuries. Dramatic advances in conventional medical science, aided by the professionalization of nursing, began to greatly improve the quality of care offered by hospitals and other infirmaries. As affluent citizens were urged by their physicians to use the ever-improving medical facilities, the number of hospitals in New York City began to rise. In 1908, there were 63 general hospitals in New York, and by 1930 there were 125.

Likewise, the emergence of the mental hygiene movement also spurred a dramatic increase in the quality of care offered to New York's mentally ill, who were admitted to the Manhattan Psychiatric Center, the world's largest mental hospital, or were transferred to improved psychiatric wards at hospitals throughout New York State. By the 1930s, 25,000 New York City residents resided in state mental institutions. Homeopathic practice, too, had substained a substantial following between 1860 and 1900, with over 100 homeopathic institutions operating in the city at the turn of the 20th century.

Congruous to the improvement of the city's public health facilities in the late 19th and early 20th centuries was the increase in public awareness of social issues relevant to public health, such as sanitation, preventive practices, and temperance. Education on these issues was facilitated by a growing number of advocate groups and charities established by the city's affluent citizenry and religious denominations.

By the early 20th century, the widescale professionalization of medical practice in New York City had firmly taken root, though several significant alterations would continue to be made to the city's public health system throughout the 20th century.