Abstract Background The rising incidence of cancer has led to an increased number of adult children impacted by parental cancer. Previous research primarily focused on younger individuals, leaving a gap in understanding the experiences of adult children aged 20–35. Objectives To examine a model that integrates the interrelationships among the disease’s characteristics (i.e., disease stage), illness representations, coping strategies, and posttraumatic growth (PTG) in young adults with parents diagnosed with cancer. In addition, we examined indirect relationships involving illness representations as independent variables, coping strategies as mediators, and PTG as the outcome variable. Purpose The rising incidence of cancer has led to an increased number of adult children impacted by parental cancer. Previous research primarily focused on younger individuals, leaving a gap in understanding the experiences of adult children aged 20–35. This study examines a model that integrates the interrelationships among the disease’s characteristics (i.e., disease stage), illness representations, coping strategies, and posttraumatic growth (PTG) in young adults with parents diagnosed with cancer. In addition, we examined indirect relationships involving illness representations as independent variables, coping strategies as mediators, and PTG as the outcome variable. Methods A cross-sectional survey was conducted with 109 adult children (ages 20–35) of cancer patients. Data were collected using the Posttraumatic Growth Inventory, the Brief Illness Perception Questionnaire, and the COPE questionnaire. Path analysis was performed to test the study’s hypotheses. Results The findings revealed that illness representations and coping strategies accounted for significant variance in PTG. Higher perceived severity of the parent’s illness was associated with greater use of problem-focused and emotion-focused coping strategies, which were linked to higher PTG. Lower perceived control over the illness was associated with less use of problem-focused coping and subsequently lower PTG. Conclusions This study underscores the importance of subjective perceptions and coping strategies in fostering PTG among young adults with parents diagnosed with cancer. The findings highlight the need for tailored psychosocial interventions to enhance adaptive illness representations and effective coping strategies, promoting resilience and growth in this unique demographic.