Dr. Schlegel is an internationally acclaimed expert in the treatment of male infertility, especially the interface of male factor treatment with assisted reproductive techniques. His work has also clarified the importance of hormonal therapy, sperm analysis and genetic studies in the evaluation of men with infertility. He was awarded the 1996 Established Clinician Award by The European Society for Human Reproduction and Embryology. He received the Barringer Medal of the American Association of Genitourinary Surgeons in 2012, and he was inducted into Johns Hopkins' Society of Scholars in 2007. He has been listed as an expert in nerve-sparing radical prostatectomy techniques as well as male infertility by Castle Connolly's "Best Doctors" Guide since 1999 as well as other national "Best Doctor" lists.

In over 300 published or submitted original manuscripts, as well as numerous book chapters and invited articles, Dr. Schlegel has described the characteristics of men who are candidates for sperm retrieval, and designed and described novel techniques for the successful achievement of pregnancy after sperm retrieval. He has also published extensively on microsurgical treatment of infertile men as well as on hormonal and genetic aspects of infertility. More importantly, the team of scientists, reproductive endocrinologists, nurses and technicians that Dr. Schlegel has worked with at Weill Cornell Medicine has achieved one of the highest pregnancy rates in the world for treatment of couples using sperm that were retrieved by Dr. Schlegel.

Early in his career, Dr. Schlegel worked with pioneers in the field of urology and male reproductive function. With Dr. Fray Marshall and Dr. Patrick Walsh at The Johns Hopkins Hospital in Baltimore, Maryland, Dr. Schlegel worked as a resident in general surgery and urology. During that time, Dr. Schlegel established some of the anatomical basis that was necessary to develop the contemporary procedure of radical prostatectomy that is used to cure localized prostate cancer. Dr. Schlegel continues to be active in the surgical treatment of prostate cancer because of his advanced understanding of this anatomy. Dr. Schlegel was granted a research scholarship from the American Foundation for Urological Disease/American Urological Association in 1989 and completed his fellowship in the area of male infertility and reproductive function with the guidance of Dr. Marc Goldstein and Dr. Wayne Bardin at The Population Council's Center for Biomedical Research at The Rockefeller University and the Center for Male Reproductive Medicine and Microsurgery in the Department of Urology at Weill Cornell Medicine in 1991.

His expertise in urology has been recognized by national and international authorities by invitations from the National Institutes of Health, The American Urologic Association, and Austrian, Australian, Brazilian, British, Chinese, Costa Rican, Emirati, French, German, Hungarian, Indonesian, Irish, Israeli, Japanese, Jordanian, Mexican, Qatari, Saudi Arabian, Turkish and Venezuelan urologic or reproductive societies to speak on issues of male infertility treatment. He has been listed in Who's Who in the World, Who's Who in America, Who's Who in the East, Who's Who in Education, Who's Who in Healthcare and Medicine, and Who's Who in Science and Engineering. He received the John K. Lattimer Award from the Kidney and Urology Foundation in 2010.

Dr. Schlegel is a former co-editor of the Journal of Andrology and has currently or previously served on editorial boards of the medical journals AUA Update Series, British Journal of Urology-International, Fertility & Sterility, Journal of Urology (Investigative Section), Techniques in Urology, Journal of Andrology and FertiliText. He was the Edwin A. Beer Program award recipient of The New York Academy of Medicine from 1996 to 1998, and received a New Investigator Award from the American Foundation for Urologic Diseases from 1993 to 1995. Dr. Schlegel serves or has served in a leadership role for several national infertility organizations, including as a council member for the American Society of Andrology Board of Directors, and a former president of the Society for Male Reproduction and Urology, as well as former president of the Society for Reproductive Surgery, former president of the Fertility Preservation Special Interest Group of the American Society of Reproductive Medicine, past president of the Society for Study of Male Reproduction of the AUA and chair of the Male Infertility Joint Guidelines Panel for AUA and ASRM. He is currently President of the American Society for Reproductive Medicine.