<sec> <title>SETTING</title> The incidence of multidrug-resistant tuberculosis (MDR-TB) is routinely reported by the Public Health England, UK, but prevalence better represents burden. </sec> <sec> <title>OBJECTIVE</title> To estimate MDR-TB prevalence, and identify the factors associated with acquired resistance and unsuccessful outcomes in people managed by the health services. </sec> <sec> <title>DESIGN</title> We included notified MDR-TB cases prevalent between 2010 and 2014. Multivariable logistic regression was used to identify the factors associated with acquisition of resistance and unsuccessful outcomes. The social risk factors (SRFs) recorded were alcohol, drug misuse, homelessness and incarceration. </sec> <sec> <title>RESULTS</title> Between 2010 and 2014, there were 2.3-3.1 times more prevalent than incident cases each year, with an increasing prevalence-to-incidence ratio over time; 86% of prevalent cases were foreign-born, and 15% had an SRF. Overall, 11% of MDR-TB cases acquired resistance, including 18% of those with SRFs and 22% of UK-born MDR-TB cases acquired resistance. Half of the cases completed treatment by 24 months; those with SRFs, extensive drug resistance or acquired resistance were less likely to complete treatment. </sec> <sec> <title>DISCUSSION</title> The number of prevalent cases is higher than incident cases, and increases over time, so a focus on prevalent cases enables better planning for services to support patients. We recommend that additional support be provided for those at risk of acquiring resistance, including those with SRFs. </sec>.