Objective: To explore what adolescent girls mean when they talk about healthiness and slimming, as well as the distinction between the 2 concepts. Design: Data was collected by the use of 8 focus groups, each with 5-9 adolescent girls. Setting: Four different schools in Oslo and 2 other municipalities in Norway in 2006-2007. Participants: Twenty-eight girls in sixth grade (11 years old) and 24 girls in tenth grade (15 years old). Analysis: Qualitative analysis. Results: The adolescent girls' knowledge about diet and physical activity was generally in accordance with recommendations for healthful diet and lifestyle. The older girls were especially interested in energy metabolism, and they had ideas about what and when to eat and how to exercise to get the most effect in terms of metabolic rate and energy expenditure. The most important difference between general healthful behavior and slimming behavior was not considered to be the behavior itself, but the mindset. The girls meant that slimming may have negative effects regardless of the healthfulness of the weight control behaviors, when the driving force is body dissatisfaction. Conclusions and Implications: The differentiation between healthiness and slimming focused more on the girls' relationship to their bodies than on behavioral differences. (Contains 1 table.)