Anxiety is common in patients undergoing radiation therapy (RT) and in their family caregivers (FCs). Little is known about individual differences in anxiety trajectories during and after RT. This study aimed to identify distinct latent classes of oncology patients and their FCs based on self-reported anxiety symptoms from the beginning to four months after the completion of RT.Using growth mixture modeling (GMM), longitudinal changes in Spielberger State Anxiety Inventory (STAI-S) scores among 167 oncology outpatients with breast, prostate, lung, or brain cancer and 85 FCs were evaluated to determine distinct anxiety symptom profiles. STAI-S scores were assessed just prior to, throughout the course of, and for four months following RT (total of 7 assessments). Baseline trait anxiety and depressive symptoms (during and after RT) were also assessed.The GMM analysis identified three latent classes of oncology patients and FCs with distinct trajectories of state anxiety: Low Stable (n = 93, 36.9%), Intermediate Decelerating (n = 82, 32.5%), and High (n = 77, 30.6%) classes. Younger participants, women, ethnic minorities, and those with children at home were more likely to be classified in the High anxiety class. Higher levels of trait anxiety and depressive symptoms, at the initiation of RT, were associated with being in the High anxiety class.Subgroups of patients and FCs with high, intermediate, and low mean levels of anxiety during and after RT were identified with GMM. Additional research is needed to better understand the heterogeneity of symptom experiences as well as comorbid symptoms in patients and FCs.