Qualitative methods were used to investigate the psychosocial experiences of young people (aged 13-21) with cancer (N=8). The experiences of young people treated in a paediatric ward were compared with those treated in adult wards. Data were collected using semi-structured interviews, observations and discussions with the treatment teams. The findings were considered in relation to two developmental theories of adolescence frequently used within this field of research: 1) Havighurst (1948), and 2) Erikson (1968). Four main themes emerged from the data: 1) personal (emotional and physical changes), 2) setting (the physical treatment environment), 3) relational (interactions with family, peers, other patients and the treatment team), and 4) education, career and the future. Differences emerged between the treatment wards in relation to young people's psychosocial experiences. The theoretical implications of the research are considered and the researcher questions the usefulness of these developmental theories within the context of young people with cancer. Alternative theories (including ideas from: positive psychology, models of chronic illness, and systemic theory) are proposed to enhance our understanding of young people's experiences during treatment. The research also discusses clinical implications, including how to enhance the provision of psychosocial care for young people with cancer.