The current study sought to: 1) assess differences in levels of physical and mental health-related quality of life (HRQOL), illness uncertainty, and intrusiveness in adolescents and young adults (AYAs) with allergies and asthma, as well as 2) examine the effect of illness appraisals on HRQOL. Participants were undergraduate students with self-reported allergies (n=74) and asthma (n=74) who completed the Mishel Uncertainty in Illness Scale (MUIS), the Illness Intrusiveness Scale (IIS), and the SF-36 Health Survey Questionnaire. Paired t-tests indicated that AYAs with allergies reported higher levels of illness uncertainty and poorer mental HRQOL than AYAs with asthma; the groups did not differ on reported levels of illness intrusiveness or physical HRQOL. Hierarchical regressions were conducted to examine the relationship between illness appraisals and HRQOL. Results revealed that poorer mental HRQOL was associated with higher illness uncertainty in AYAs with allergies and higher illness intrusiveness in AYAs with asthma. Poorer physical HRQOL was associated with higher illness uncertainty in AYAs with asthma and higher illness intrusiveness in AYAs with allergies and asthma. The current examination suggests that illness appraisals may be differentially related to HRQOL in AYAs with allergies compared to those with asthma.