Introduction Research suggests that girls who reach menarche at an early age are at greater risk for negative sexual and reproductive health (SRH) outcomes than their later‐maturing counterparts, but very little research has examined this issue in sub‐Saharan Africa, especially in West Africa. The goal of the current study was to determine whether early menarche was associated with any SRH outcomes in a sample of Ghanaian girls. Methods The study data were drawn from the baseline assessment of a longitudinal study involving two age cohorts (13–14 and 18–19 years) of 700 adolescent girls from Ghana. Logistic regressions were used to assess the association between early menarche (before age 13) and seven SRH outcomes (adolescent sexual activity, early sexual initiation, inconsistent condom use, transactional sex, sexual violence, multiple sexual partners, and adolescent pregnancy). Results Early menarche was significantly associated with adolescent sexual activity (odds ratio OR = 6.4; 95% confidence interval CI 2.1–19.7), and sexual violence (OR = 3.2; 95% CI 1.6–6.2) in the younger cohort and early sexual initiation (OR = 3.2; 95% CI 1.19–8.61) and multiple sexual partners (OR = 3.7; 95% CI 1.39–9.87) in the older cohort. Early menarche was also associated with transactional sex and teen pregnancy in the full sample. Conclusions These findings suggest the need for special attention to the needs of early‐maturing girls in SRH programming. Interventions are needed to delay adolescent sexual activity in girls with early menarche. Efforts to prevent sexual violence among adolescent girls in Ghana may benefit from targeting and addressing the specific needs of early‐maturing girls.