BackgroundUnderweight among women of reproductive age poses significant health risks. Despite global and national reductions, it remains a public health concern in Rwanda. ObjectivesThis study assessed the prevalence and associated factors of underweight among Rwandan women of reproductive age.MethodsA cross-sectional analysis was used on data from the 2019-2020 Rwanda Demographic and Health Survey (RDHS), involving a nationally representative sample of 6,831 women aged 15-49 years. Data was collected through questionnaires and anthropometric measurements. A weighted analysis and multivariable analysis were performed. ResultsThe prevalence of underweight was 5.8% (95% CI: 5.26-6.46). Women aged 15-24 years had higher odds of being underweight (AOR: 1.54, 95% CI: 1.21-1.95), while those aged 25-34 years had lower odds of being underweight (AOR: 0.67, 95% CI: 0.47-0.94). Moreover, women from rural (AOR: 1.76, 95% CI: 1.25-2.49), from poor household (AOR: 1.74, 95% CI: 1.35-2.25), middle-class households (AOR: 1.42, 95% CI: 1.05-1.93) and being anemic (AOR: 1.40, 95% CI: 1.04-1.87) were more likely to be underweight.ConclusionsAlthough underweight prevalence was low, younger women, rural residents, and those from lower socioeconomic status or with anaemia were at greater risk. These findings underscore the need for targeted interventions addressing both nutritional and broader social determinants of health. Rwanda J Med Health Sci 2025;8(2):332-342