Objective Concurrent sexual partnerships (CP) have been identified as a potential driver in the HIV epidemic in southern Africa, making it essential to understand motivating factors for engagement in CP. We aimed to assess community attitudes and beliefs about relationship factors that influence men and women in stable relationships to engage in CP in Tanzania. Social exchange theory was used for interpreting the data.

Design Qualitative study with focus group discussions (FGDs).

Setting Semiurban/rural communities in four regions across Tanzania (Dar es Salaam, Shinyanga, Iringa and Mbeya).

Participants 120 women aged 17–45 years and 111 men aged 18–49 years from four study areas participated in 32 FGDs.

Outcome measures FGD participants were asked the following questions about CP: definitions and types, motivations and justifications for engaging or not engaging, cultural factors, gender and socialisation, and local resources and efforts available for addressing CP. Our analysis focused specifically on beliefs about how relationship factors influence engagement in CP.

Results Dissatisfaction with a stable relationship was believed to be a contributing factor for engagement in CP for both men and women. Participants more commonly reported financial dissatisfaction as a contributing factor for women engaging in CP within stable relationships, whereas emotional and sexual dissatisfaction were reported as contributing factors for men and women. Furthermore, participants described how potential outside partners are often evaluated based on what they are able to offer compared with stable partners.

Conclusions Efforts to reach men and women in stable relationships with HIV prevention messages must consider the various dimensions of motivation for engaging in CP, including relationship dynamics.