Thomeer’s research topics include aging, family, health, gender, and sexuality. She addresses questions about how relationships influence and are influenced by physical and mental health, with particular attention to gender and sexuality. She uses both qualitative and quantitative methods, emphasizing dyadic methods. For example, past studies consider how one person’s depression impacts his/her spouse’s mental health, what intimacy looks like in gay, lesbian, and straight relationships, how nursing home admission rates differ across racial/ethnic groups, and how parenthood changes health habits. In her current research, she focuses on caregiving within couples in which both spouses have functional limitations, the role of wealth in explaining racial and marital disparities in mortality, and gender identity development among same-sex and different-sex couples. She currently serves on the editorial board of the Journal of Marriage and Family and Society and Mental Health.