Upon his return from Europe, he became the Medical Director at the Philadelphia Hospital for Mental Disorder and served in this position from 1920 to 1922.
During those years, he also served as director of Hospital Service for the National Committee for Mental Hygiene, a voluntary lay organization.
This period began a career of surveys of public mental hospitals under the auspices of the National Committee for Mental Hygiene and later, the American Psychiatric Association, the American Neurological Association, the U.S. Public Health Service, and the Rockefeller Foundation.
The public mental hospitals in the various states had become overcrowded, understaffed, and received inadequate funding.
In 1935, the American Medical Association (AMA) began an investigation at the instigation of its Mental Health committee.
The AMA surveys were discontinued and only a statistical report of the findings was published, with no known further action.
Following his U.S. Army service during World War II, Hamilton accepted the position as Superintendent of the Essex Overbrook Hospital in New Jersey.
He served as an advisor to the U.S. Public Health Service from 1939 to 1947, and was an active participant in the founding of the American Board of Psychiatry and Neurology.
"Review of Infective-Exhaustive Psychoses with Special Reference to Subdivision and Prognosis," American Journal of Psychiatry 66(4) (April 1910): 579–586.
Report of the Rhode Island Mental Hygiene Survey, requested by Governor Emery J. San Souci and by the Penal and Charitable Commission.
"The Psychiatric Resources of New York: A Brief Description for those Attending the 1934 Meeting," American Journal of Psychiatry 90(5) (March 1934): 1097–1128.
Hamilton, Samuel Warren, et al. A Study of the Public Mental Hospitals of the United States, 1937-39.