This study examined a moderated mediation model testing whether dysmorphic concern is related to behaviour altered to change appearance. This relationship is potentially mediated by depressive symptomatology (dysphoria and self‐esteem) and ideas of reference about “laughing, commenting” and “attention, appearance,” and each mediated relationship moderated by sex. The sample was made up of 3377 adolescents from 12 to 18 years old (Mage = 14.52; SD = 1.65, 56.5% girls). The results showed that dysphoria and ideas of reference about “laughing, commenting” and “attention, appearance” partially mediated the relationship between dysmorphic concern and behavioural impairment related to body image. The relationship with dysphoria was moderated by sex, such that the mediation effect was stronger in girls than in boys. This result implies that girls who are worried about some characteristic of their appearance and show dysphoria are at greater risk of altered behaviour involving avoidance or controlling their appearance than boys. In addition, a possible risk of body dysmorphic disorder (3.45% of the sample) was found, with very prominent hiding behaviour using clothing or control behaviours, such as frequent weighing and looking at oneself in the mirror too much. Implications of these findings are discussed.