Background In 2017, India was home to nearly 20% of maternal and child deaths occurring globally. Accredited social health activists (ASHAs) act as the frontline for health services delivery in India, providing a range of reproductive, maternal, newborn, child health, and nutrition (RMNCH&N) services. Empirical evidence on ASHAs' knowledge is limited, yet is a critical determinant of the quality of health services provided. We assessed the determinants of RMNCH&N knowledge among ASHAs and examined the reliability of alternative modalities of survey delivery, including face-to-face and caller attended telephone interviews (phone surveys) in 4 districts of Madhya Pradesh, India. Methods We carried out face-to-face surveys among a random cross-sectional sample of ASHAs (n = 1,552), and administered a follow-up test-retest survey within 2 weeks of the initial survey to a subsample of ASHAs (n = 173). We interviewed a separate sub-sample of ASHAs 2 weeks of the face-to-face interview over the phone (n = 155). Analyses included bivariate analyses, multivariable linear regression, and prevalence and bias adjusted kappa analyses. Findings The average ASHA knowledge score was 64% and ranged across sub-domains from 71% for essential newborn care, 71% for WASH/ diarrhea, 64% for infant feeding, 61% for family planning, and 60% for maternal health. Leading determinants of knowledge included geographic location, age <30 years of age, education, experience as an ASHA, completion of seven or more client visits weekly, phone ownership and use as a communication tool for