She researched retrovirology, immunology, and genetics at Stanford University where she completed a master's degree in medical microbiology.[2][3] In 1975, Mathieson earned a doctor philosophy in biology from the Memorial Sloan Kettering Cancer Center and Weill Cornell Medicine of Cornell University in New York City.[2] Her dissertation was titled Selective expression of surface components on differentiated cells of the mouse: immunoselection of Y-bearing sperm in an in vitro fertilization system and expression of the thymocyte surface markers G(IX), TL and LY in tetraparental mice.[4] She was a post-doctoral researcher and staff fellow at National Institute of Allergy and Infectious Diseases (NIAID) where she researched lymphocyte surface markers and T cell subsets from 1975 to 1982.[2]