Underwood wished to continue enter the medical profession, and gained the attention of eminent surgeon Sir Cæsar Hawkins, 1st Baronet, who had served as sergeant-surgeon to George II.
"[2] After living briefly in Paris, Underwood became a member of the Surgeon's Company and established a practice in both surgery and obstetrics in Margaret Street, Cavendish Square.
[3] In 1783, Underwood published Treatise upon ulcers of the legs, scrophulous sores and mammary abscesses (1783), "in which former methods of treatment were candidly examined and compared, with one more rational and safe, proving that a perfect cure may generally be effected more certainly, without rest and confinement, than by the strict regimen in common use."
He included "an introduction on the process of ulceration and the origin of pus laudabile: to which are added hints on a successful method of treating some scrophulous tumors and the mammary abscess and sore nipples of lying-in women."
[11] A review from The Literary Chronicle noted: [It] embraces a period of more than sixty years, during which it was the constant practice of Dr. Underwood to commit to paper the occurrences of each day for his own personal gratification; his domestic circumstances, professional visits, religious impressions, and Christian duties, were all entered as in a day-book without any regard to order or arrangement.
"[13] The work was said to be mournful at times, and another review in The London Literary Gazette said that "its author seems to have overshadowed and bewildered his mind by painful metaphysical contemplation of the greatest mysteries of religion; but he displays a Christian, if a too intense, anxiety to arrive at truth and satisfy his soul.