In parliament, Oomen-Ruijten first served on the Committee on the Environment, Public Health and Consumer Protection (1989-2004) and the temporary Committee on Genetics (2001). Furthermore, she was also a member of the Committee on Employment and Social Affairs (1994-1999, 2004–2007) and the Committee on Equal Rights of Women. Later, she was a member of the Committee on Foreign Affairs (from 2007) and its Subcommittee on Human Rights (from 2009) Among other assignments, she was the European Parliament's rapporteur on the possible accession of Turkey to the European Union, on pension rights of EU citizens on measures against cervical cancer, and on cutting emissions from plants powered by coal and oil.