An adequate food intake, in terms of quantity and quality, is a key to healthy life. Malnutrition is the most serious consequence of food insecurity and has a multitude of health and economic implications. India has the world's largest population living in slums, and these have largely been underserved areas. The State of Food Insecurity in the World (2012) estimates that India is home to more than 217 million undernourished people. Various studies have been conducted to assess food insecurity at the global level; however, the literature is limited as far as India is concerned. The present study was conducted with the objective of documenting the prevalence of food insecurity at the household level and the factors determining its existence in an urban slum population of northern India. This cross-sectional study was conducted in an urban resettlement colony of South Delhi, India. A pre-designed, pre-tested, semi-structured questionnaire was used for collecting socioeconomic details and information regarding dietary practices. Food insecurity was assessed using Household Food Insecurity Access Scale (HFIAS). Logistic regression analysis was performed to determine the factors associated with food insecurity. A total of 250 women were interviewed through house-to-house survey. Majority of the households were having a nuclear family (61.6%), with mean family-size being 5.5 (SD +/- 2.5) and the mean monthly household income being INR 9,784 (SD +/- 631). Nearly half (53.3%) of the mean monthly household income was spent on food. The study found that a total of 77.2% households were food-insecure, with 49.2% households being mildly food-insecure, 18.8% of the households being moderately food-insecure, and 9.2% of the households being severely food-insecure. Higher education of the women handling food (OR 0.37, 95% CI 0.15-0.92; p < or = 0.03) and number of earning members in the household (OR 0.68, 95% CI 0.48-0.98; p < or = 0.04) were associated with lesser chance/odds of being food-insecure. The study demonstrated a high prevalence of food insecurity in the marginalized section of the urban society. The Government of India needs to adopt urgent measures to combat this problem.