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. .