We conducted a survey of cooking fat usage in a representative sample of mothers from low and middle income families in Bogota, Colombia (n=2368). The fatty acid composition of the most commonly available cooking fats (n=30) in the market was analyzed by gas chromatography. 87% of the surveyed population consumed at least one of these 30 cooking fats. The types of fat primarily used for cooking were mixed vegetable oils, 69%; sunflower oil, 22%; margarine, 2.4%; palm shortening, 2.8%; and chicken fat, 1.4%. The trans fat content of sunflower oil was unexpectedly high (mean, 4.2%; range, 2.2–8.6), compared to that in the vegetable mixtures (mean, 2.6%; range, 1.2–5.1). Overall, 35% and 18% of the families used cooking fats with >2% and >4% trans fatty acids, respectively. In multivariate analysis, usage of sunflower oil as the primary cooking fat was positively related to the number of household assets, the amount of money spent on food per person/day at home, and maternal education and inversely associated with an index of household food insecurity. Paradoxically, oblivious to the high trans content of sunflower oil, “health” was the main reason reported by the mothers to choose sunflower over other oils. The high trans content of sunflower oil, and the belief that sunflower oil is healthier than others may result in an elevated intake of transfats. Regulation of trans fat content in foods is urgently needed in Colombia.