In adolescence, girls experience a concerning drop in their mental health and wellbeing. I argue here that their tendency to ‘internalise’ in the face of adversity and to ‘languish’ rather than ‘flourish’, is heavily influenced by their developmental histories of gender role socialisation, compounded by the specific socialisation pressures they face in adolescence, particularly concerning body image and harassment from male and female peers. Although we are often said to live in post-feminist times, there is ongoing evidence that girls and women in the West as well as around the world continue to be disadvantaged by patriarchal social systems. In the context of psychology's positivist and individualist history, and its current privileging of biological explanations, clinical psychology neglects the role of patriarchy and gender socialisation in undermining adolescent girls' mental health and wellbeing. A resurgence of efforts to incorporate feminism into clinical practice would be timely, given the current cultural push in the West for acceptance of more diverse and fluid gender identities.