Purpose To determine the effects of patient age and comorbidity level on life expectancy (LE) benefits associated with imaging follow-up of Bosniak IIF renal cysts and pancreatic side-branch (SB) intraductal papillary mucinous neoplasms (IPMNs). Materials and Methods A decision-analytic Markov model to evaluate LE benefits was developed. Hypothetical cohorts with varied age (60-80 years) and comorbidities (none, mild, moderate, or severe) were evaluated. For each finding, LE projections from two strategies were compared: imaging follow-up and no imaging follow-up. Under follow-up, it was assumed that cancers associated with the incidental finding were successfully treated before they spread. For patients without follow-up, mortality risks from Bosniak IIF cysts (renal cell carcinoma) and SBIPMNs (pancreatic ductal adenocarcinoma) were incorporated. Model assumptions and parameter uncertainty were evaluated in sensitivity analysis. Results In the youngest, healthiest cohorts (age, 60 years; no comorbidities), projected LE benefits from follow-up were as follows: Bosniak IIF cyst, 6.5 months (women) and 5.8 months (men); SBIPMN, 6.4 months (women) and 5.3 months (men). Follow-up of Bosniak IIF cysts in 60-year-old women with severe comorbidities yielded a LE benefit of 3.9 months; in 80-year-old women with no comorbidities, the benefit was 2.8 months, and with severe comorbidities the benefit was 1.5 months. Similar trends were observed in men and for SBIPMN. Results were sensitive to the performance of follow-up for cancer detection; malignancy risks; and stage at presentation of malignant, unfollowed Bosniak IIF cysts. Conclusion With progression of age and comorbidity level, follow-up of low-risk incidental findings yields increasingly limited benefits for patients. © RSNA, 2018 Online supplemental material is available for this article.