Many female sex workers begin sex work as mothers, or because they are mothers, and others seek childbearing. Motherhood may influence women's livelihoods as sex workers and their subsequent HIV risks. We used qualitative research methods (30 in-depth interviews and three focus group discussions) and employed Connell's theory of Gender and Power to explore the intersections between motherhood, sex work, and HIV-related risk. Participants were adult women who self-reported exchanging sex for money within the past month and worked in entertainment venues in southern Tanzania. Participants had two children on average, and two-thirds had children at home. Women situated their socially stigmatised work within their respectable identities as mothers caring for their children. Being mothers affected sex workers' negotiating power in complex manners, which led to both reported increases in HIV-related risk behaviours (accepting more clients, accepting more money for no condom, anal sex), and decreases in risk behaviours (using condoms, demanding condom use, testing for HIV). Sex workers/mothers were aware of risks at work, but with children to support, their choices were constrained. Future policies and programming should consider sex workers' financial and practical needs as mothers, including those related to their children such as school fees and childcare.