CONTEXT: The relationship of national laws that prohibit child marriage with the prevalence of child marriage and adolescent birth is not well understood. METHODS: Data from Demographic and Health Surveys and from the Child Marriage Database created by the MACHEquity program at McGill University were used to examine the relationship between laws that consistently set the age for marriage for girls at 18 or older and the prevalence of child marriage and teenage childbearing in 12 Sub-Saharan African countries. Countries were considered to have consistent laws against child marriage if they required females to be 18 or older to marry, to marry with parental consent and to consent to sex. Associations between consistent laws and the two outcomes were identified using multivariate regression models. RESULTS: Four of the 12 countries had laws that consistently set the minimum age for marriage at 18 or older. After adjustment for covariates, the prevalence of child marriage was 40% lower in countries with consistent laws against child marriage than in countries without consistent laws against the practice (prevalence ratio, 0.6). The prevalence of teenage childbearing was 25% lower in countries with consistent minimum marriage age laws than in countries without consistent laws (0.8). CONCLUSION: Our results support the hypothesis that consistent minimum marriage age laws protect against the exploitation of girls.