Background Neonatal and maternal mortality rates remain high in Kenya. Knowledge of neonatal danger signs may reduce delay in deciding to seek care. Evidence is emerging on the influential role of male partners in improving maternal and newborn health. This study analysed the factors that determine men’s and women’s knowledge and practices in postnatal and neonatal care-seeking, in order to inform design of future interventions. Methods A quantitative, cross-sectional study was undertaken in Bungoma County, Kenya. Women who had recently given birth (n = 348) and men whose wives had recently given birth (n = 82) completed questionnaires on knowledge and care-seeking practices relating to the postnatal period. Univariate and multivariate logistic regression analyses were performed to investigate associations with key maternal and newborn health outcomes. Results 51.2% of women and 50.0% of men knew at least one neonatal danger sign, however women knew more individual danger signs than men. In the univariate model, women’s knowledge of a least one neonatal danger sign was associated with attending antenatal care ≥4 times (OR 4.46, 95%CI 2.73–7.29, p<0.001), facility birth (OR 3.26, 95%CI 1.89–5.72, p<0.001), and having a male partner accompany them to antenatal care (OR 3.34, 95%CI 1.35–8.27, p = 0.009). Higher monthly household income (≥10,000KSh, approximately US$100) was associated with facility delivery (AOR 11.99, 95%CI 1.59–90.40, p = 0.009). Conclusion Knowledge of neonatal danger signs was low, however there was an association between knowledge of danger signs and increased healthcare service use, including male partner involvement in antenatal care. Future interventions should consider the extra costs of facility delivery and the barriers to men participating in antenatal and postnatal care.