Objective To analyse patterns of knowledge, comprehension, attitudes and practices regarding the traffic light label placed on processed food packages to inform Ecuadorian consumers about levels of added fat, sugar and salt. Design Twenty-one focus group discussions organized by age group, sex and place of residence. Interviews with representatives of companies that manufacture or market processed foods. Analysis of regulations and structured observations of processed food labels. Setting Cities and towns in Ecuador's coastal, highland and eastern lowland regions. Subjects One hundred and seventy-eight participants in twenty-one focus group discussions and nine key informants. Results Focus group participants knew about the traffic light label and understood the information it conveys, but not all changed their attitudes and practices related to the purchase and consumption of processed foods. Children, adolescents and adult males reported using the information infrequently; adolescents interested in health and adult women used the label the most to select products. Representatives of companies that manufacture or market processed foods generally opposed the policy, stating that the information is misleading. Nevertheless, some companies have reduced levels of added fat, sugar or salt in their products. Conclusions The traffic light label is an effective tool for conveying complex information. Its potential contribution to reduce consumption of products with high levels of fat, sugar and salt could be enhanced by promoting healthy diets among consumers who have not changed purchasing and consumption behaviour, by placing the label on front panels and by monitoring the production and marketing of processed foods.