BACKGROUND Cigarette smoking and depression are associated with morbidity and mortality. Among veterans, approximately 22% are current smokers and 11%-15% have been diagnosed with depression. Although prior research suggests a strong association between smoking and depression among veterans, little research has examined trajectories of smoking and depressive symptoms and their correlates over time in this population. OBJECTIVE Using parallel process growth curve modeling, we examined the longitudinal relationship between smoking and depression and tested whether posttraumatic stress disorder (PTSD) symptoms predict smoking and depression trajectories over 18 months (February 2020-August 2021). Veterans were recruited for an online, longitudinal study and responded to surveys across five-time points (baseline N = 1230; retention = 79.3%-83.3% across waves). RESULTS Associations indicated that more frequent smoking at baseline was associated with steeper increases in depression symptom severity, and greater depression severity at baseline was associated with a less steep decrease in smoking frequency over time. PTSD was associated with less smoking at time 1 but more frequent smoking at times 3-5 as well as greater depression across all time points. CONCLUSIONS Findings provide support that the growth trajectories of smoking and depression are linked, and PTSD symptoms are associated with these trajectories among veterans. Addressing these factors simultaneously in veteran treatment centers or through tobacco cessation efforts may be beneficial. CONCLUSIONS This study offers strong evidence that the growth trajectories of smoking and depression are linked, and PTSD symptoms affect these trajectories among veterans, who represent a largely understudied population despite high rates of substance use and mental health problems. Results of this study strengthen the case for a more integrated treatment approach in which both smoking and mental health concerns are simultaneously addressed, which may yield more beneficial physical health and clinical outcomes for post-9/11 veterans.