Few studies describe supportive care needs among young adults (YAs) with cancer ages 25 to 39 using validated questionnaires. Previous findings identified the need for psychological and information support and suggest that gender, age, psychological distress, and coping may be associated with greater need for this support. To substantiate these findings, this study aimed to (1) describe the supportive care needs of YAs in each domain of the Supportive Care Needs Survey and (2) explore the relationship between unmet supportive care needs and clinical and demographic factors, health-related quality of life, psychological distress, illness cognitions, and service needs using latent class analysis. Clinical teams from six hospitals in England invited eligible patients to a cross-sectional survey by post. A total of 317 participants completed the survey online or on paper. YAs expressed the most need in the psychological and sexuality domains. Using latent class analysis, we identified three classes of YAs based on level of supportive care need: no need (53.3%), low need (28.3%), and moderate need (18.4%). In each class, median domain scores in each domain were similar. Low and moderate need classes were associated with worse health-related quality of life and greater helplessness. Unmet service needs were associated with the moderate-need class only. Patients with unmet supportive care needs should be offered holistic care across supportive care domains.