Background Women across the world are mistreated during childbirth. We aimed to develop and implement evidenceinformed, validated tools to measure mistreatment during childbirth, and report results from a cross-sectional study in four low-income and middle-income countries. MethodsWe prospectively recruited women aged at least 15 years in twelve health facilities (three per country) in Ghana, Guinea, Myanmar, and Nigeria between Sept 19, 2016, and Jan 18, 2018. Continuous observations of labour and childbirth were done from admission up to 2 h post partum. Surveys were administered by interviewers in the community to women up to 8 weeks post partum. Labour observations were not done in Myanmar. Data were collected on sociodemographics, obstetric history, and experiences of mistreatment. Findings 2016 labour observations and 2672 surveys were done. 838 (41•6%) of 2016 observed women and 945 (35•4%) of 2672 surveyed women experienced physical or verbal abuse, or stigma or discrimination. Physical and verbal abuse peaked 30 min before birth until 15 min after birth (observation). Many women did not consent for episiotomy (observation: 190 [75•1%] of 253; survey: 295 [56•1%] of 526) or caesarean section (observation: 35 [13•4%] of 261; survey: 52 [10•8%] of 483), despite receiving these procedures. 133 (5•0%) of 2672 women or their babies were detained in the facility because they were unable to pay the bill (survey). Younger age (15-19 years)and lack of education were the primary determinants of mistreatment (survey). For example, younger women with no education (odds ratio [OR] 3•6, 95% CI 1•6-8•0) and younger women with some education (OR 1•6, 1•1-2•3) were more likely to experience verbal abuse, compared with older women (≥30 years), adjusting for marital status and parity.Interpretation More than a third of women experienced mistreatment and were particularly vulnerable around the time of birth. Women who were younger and less educated were most at risk, suggesting inequalities in how women are treated during childbirth. Understanding drivers and structural dimensions of mistreatment, including gender and social inequalities, is essential to ensure that interventions adequately account for the broader context.