Multiple sclerosis (MS) is a chronic neurological disease primarily diagnosed in young adulthood. However, a proportion of MS patients have onset during childhood and adolescence. Very little is known about the psychosocial impact of MS on this population. This qualitative study explored the psychosocial experiences of adolescents with early-onset MS. In particular, an emphasis was placed on examining peer relationships and social behaviours in relation to these experiences. Data analysis was derived from grounded theory, which provided a framework for examining and categorizing interview data into themes. The categories were then constructed logically and systematically into a theoretical model which represented the data. Through this innovative grounded theory, a theoretical paradigm for understanding the psychosocial experiences of adolescents with MS was developed. Two primary conclusions were drawn from the theory relating to the significance of grief in understanding psychosocial experiences in adolescents with MS and the influential role of peer relationships in this grief process.