ObjectivesTo examine how work-related mobility among female sex workers (FSWs) is associated with gender-based violence (GBV) in Iringa, Tanzania.DesignCross-sectional analyses were conducted on baseline data gathered between October 2015 and April 2016 from FSWs participating in Project Shikamana, a community empowerment-based combination HIV prevention intervention.SettingParticipants were recruited for the baseline study using venue-based time-location sampling in two communities in Iringa, Tanzania.ParticipantsFSWs were eligible for participation if they were 18 years or older and had exchanged sex for money within the past month. Four-hundred ninety-six FSWs participated in the baseline survey.Primary and secondary outcome measuresAny recent experience of GBV was examined by recent work-related mobility among FSWs. Any recent experience of GBV was also disaggregated by severity for analyses. All bivariate and multivariate binary and multinomial logistic regressions adjusted for intraclass correlations among women recruited from the same venues.ResultsForty per cent of participants experienced recent physical or sexual violence, and 30% recently experienced severe physical or sexual violence. Thirty-three per cent of participants recently exchanged sex for money outside of their district or region, and 12% were both intraregionally and inter-regionally mobile for sex work. Intraregionally and inter-regionally mobile FSWs had 1.9 times greater odds of reporting recent GBV (adjusted OR: 1.89; 95% CI: 1.06 to 3.38; p=0.031) compared with non-mobile FSWs and a 2.5 times higher relative risk for recent experience of severe GBV relative to no recent GBV (relative risk ratio: 2.51; 95% CI: 1.33 to 4.74; p=0.005).ConclusionsMobility for sex work may increase FSWs’ exposure to GBV, particularly more severe GBV. The vulnerability of mobile FSWs to violence, particularly severe forms, demands inclusive services that are accessible to mobile FSWs.