BACKGROUND The burden of food insecurity in Portugal, and the socioeconomic and demographic factors that are related to this condition, are unknown. OBJECTIVE To evaluate the frequency of food insecurity and to identify its associated characteristics in the Portuguese population. METHODS Data from 3,552 heads of family respondents of the 2005/06 Portuguese National Health Survey were analyzed in a cross-sectional study. Food insecurity was evaluated with the use of the US Department of Agriculture Household Food Security Survey Module 6-Item Short Form. Chi-square tests and multivariate logistic regression models were conducted. Significance was indicated at p < .05. RESULTS Among the respondents, 16.5% were food insecure and 3.5% had very low food security. The odds of being food insecure were highest for women (OR, 1.51; 95% CI, 1.20 to 1.91), smokers (OR, 1.56; 95% CI, 1.20 to 2.02), younger people (OR, 2.54; 95% CI, 1.69 to 3.80), unemployed people (OR, 3.04; 95% CI, 2.01 to 4.60), those with lower education (OR, 7.98; 95% CI, 4.73 to 13.49), and those with lower income (OR, 6.27; 95% CI, 4.23 to 9.30). CONCLUSIONS The present study explored for the first time the burden of food insecurity in Portugal, revealing that it was highly prevalent, affecting one in six Portuguese citizens. Low education and low income were the main factors associated with food insecurity.