Juan Rosai (August 20, 1940 – July 7, 2020) was an Italian-born American physician who contributed to clinical research and education in the specialty of surgical pathology.

He was the principal author and editor of a major textbook in that field, and he characterized novel medical conditions such as Rosai-Dorfman disease and the desmoplastic small round cell tumor.

While serving subsequently as a house officer in pathology at the Regional Hospital of Mar del Plata, Rosai was introduced to Lauren Ackerman at a medical conference in Argentina.

Rosai completed his residency and fellowship in anatomic pathology at Washington University School of Medicine and Barnes Hospital under Lauren Ackerman's mentoring.

[3] From 1991 to 1999, Rosai was the James Ewing Alumni Professor and Chairman of Pathology at Memorial Sloan-Kettering Cancer Center in New York City.

During his work in Italy, Rosai maintained academic connections to the United States as adjunct professor of pathology at the Weill Cornell Medical College of Cornell University, visiting professor of pathology at Harvard University and Massachusetts General Hospital, and senior consulting pathologist at Genzyme Genetics (LabCorp).

Rosai was an author of more than 400 scientific peer-reviewed papers on topics in pathology,[4] including the seminal descriptions of entities such as sinus histiocytosis with massive lymphadenopathy (Rosai-Dorfman disease), desmoplastic small round cell tumor, spindle-cell epithelial tumor with thymus-like differentiation of the thyroid, and sclerosing angiomatoid nodular transformation of the spleen.