Subclinical mastitis (SCM) is an asymptomatic inflammation of mammary tissue and has been associated with lactation failure, suboptimal growth in early infancy, and increased risk of mother-to-child transmission of HIV via breast milk. A rapid survey was carried out to determine the prevalence of SCM among lactating Ghanaian women between 3 and 4 months postpartum. Bilateral breast milk samples were obtained from 117 lactating women in Manya Krobo, Ghana and analyzed for sodium (Na) and potassium (K). An elevated sodium/potassium ratio (Na/K) above 1.0 was considered indicative of SCM. Overall, SCM prevalence was observed among 45.3% of the women. About 30% of the women had unilateral SCM. Na/K was associated with maternal age. The high SCM prevalence in Manya Krobo suggests the need for lactation support to reduce SCM and the risk of poor infant outcomes.