What is Bernadette's maiden surname?

Bernadette's maiden surname is Rostenkowski.

Before marrying Howard Wolowitz, Bernadette is known as Bernadette Rostenkowski. After their marriage, the character is generally identified as Bernadette Rostenkowski-Wolowitz, preserving her birth surname in a hyphenated married name.

Bernadette is introduced as Penny's co-worker at the Cheesecake Factory while paying her way through graduate school. She later earns a doctorate in microbiology and works for a pharmaceutical company, giving the show another scientist whose career is distinct from the physicists and engineer in the main group.

The surname can be easy to miss because the character is often called simply Bernadette, and her married name appears frequently later in the series. Koothrappali belongs to Raj, Fowler belongs to Amy, and Hofstadter belongs to Leonard; none is Bernadette's family name.