ObjectivesTo estimate the prevalence and identify the factors associated with undiagnosed hypertension in India. Study designA secondary data analysis using the National Family Health Survey (NFHS-5) covering the period 2019–2021. MethodsInformation on hypertension among individuals aged 15–49 years was extracted from the survey dataset. We estimated the prevalence of undiagnosed hypertension using physical measurements along with self-reported data from the survey. A log-binomial model with survey-adjusted Poisson regression was used to estimate the prevalence ratio between undiagnosed and diagnosed hypertension. Multinomial logistic regression analysis examined the factors associated with diagnosed hypertension (vs healthy) and undiagnosed hypertension (vs healthy). All the analyses were survey-weight adjusted and stratified by gender. ResultsThe survey-adjusted prevalence of undiagnosed hypertension was 8.75% (8.62%–8.87%) and was higher among males [13.56% (13.03%–14.12%)] than in females [8.14% (8.03%–8.25%)]. The proportion of individuals with undiagnosed hypertension among total hypertension was 44.99% (44.44%–45.55%) and was higher in males [65.94% (64.25%–67.60%)] than in females [42.18% (41.66%–42.71%)]. ConclusionsOur findings revealed that age, higher body mass index, no access to health care, and having no comorbidities were risk factors for undiagnosed hypertension. One in twelve people had undiagnosed hypertension, and of those with hypertension, one in two were undiagnosed, with males being disproportionately affected. Targeted public health interventions are crucial to improve hypertension screening, particularly among middle-aged and obese individuals without comorbidities.