Although most research linking health disadvantage with gender has focused on women, recent work indicates that hegemonic masculinities can also place the health of men at risk. The importance of comparing the experiences of women and men has been emphasised and this paper focuses on the ways in which the social constructions of femininities and masculinities affect how teenagers live with asthma or diabetes. The majority of girls incorporated these conditions and the associated treatment regimens into their social and personal identities, showing a greater adaptability to living with asthma or diabetes. However, this could have detrimental effects in terms of control, as girls sometimes lowered expectations for themselves. In addition, two aspects of the treatment regimens, diet and exercise, were found to disadvantage girls and advantage boys, because of contemporary meanings of femininities and masculinities. The social construction of femininities meant that these conditions were not seen as the threat that they were by the majority of boys interviewed, who made every effort to keep both conditions outside their personal and social identities by passing. The majority of boys maintained a 'valued' identity by feeling in control of their body and their condition. However, for the small minority of boys who were no longer able to pass the impact of chronic illness led to a 'disparaged' identity. The interaction of gender and health is seen as a complex two-way process, with aspects of contemporary femininities and masculinities impacting on the management of these conditions, and aspects of these conditions impacting in gendered ways upon the constructions of gender.