Background: Coping efficacy and social isolation are each uniquely related to social well-being among those with lung cancer, yet little is known how they fluctuate in the context of one’s CT scan. For the present study, researchers tested the cross-sectional relationship between social isolation and social well-being, as well as the longitudinal relationship between monthly coping efficacy and social well-being in the months before one’s CT scan. Methods: 25 patients with lung cancer who were within 6 months of their upcoming CT scan were recruited. These participants were predominantly white (80%; Black: 12%), women (96%), and were between 43 and 78 years old (M = 62.33, SD = 8.10). Baseline surveys asked about demographic information and social isolation; the repeated monthly surveys asked about coping efficacy and social well-being every 30 days until one’s scan. Results: During months when participants reported high coping efficacy, they also reported increases in social well-being (γ10 = 0.07, t = 2.44, p = .02). In addition, if the participant reported high levels of social isolation at baseline, they reported low levels of social well-being (γ01 = -0.63, t = -3.01, p = .007). Our model accounted for 10.53% of the within-person variance, and 26.65% of the between-person variance, in monthly social well-being. Conclusions: This longitudinal study was the first to look at how social isolation and coping efficacy relate to social well-being in a cancer-specific context. That is, among those with lung cancer who are approaching their upcoming CT scans. Future research should identify specific mechanisms to intervene that could help patients with lung cancer improve their social well-being as they approach their recurrent scans.