Background <p>Mental adjustment to cancer is an important factor for patients to change their lives by coping with cancer. This study aimed to identify the prevalence and predictors of mental adjustment to cancer in patients who were scheduled to undergo resection for non-small cell lung cancer (NSCLC) in Korea.</p> Methods <p>A total of 691 patients were recruited from September 2021 to October 2022. Poor mental adjustment to cancer was defined by the above or below the 25th percentile of the mean score in each subscale of the Korean version of Mini-Mental Adjustment to Cancer (K-Mini-MAC).</p> Results <p>The mean age of the study population was 63.2 ± 9.3&#xa0;years, and approximately half (50.5%) were male. Among our subjects who were operable, poor mental adjustment was prominent in the Anxious Preoccupation (AP) subscale, but not in the Helpless/Hopeless (HH) subscale. Poor mental adjustment in the HH subscale was predicted based on unemployed status and anxiety. Poor mental adjustment in the AP subscale was predicted based on young age, non-alcohol drinker, and anxiety. Poor mental adjustment in the novel Positive Attitudes (PA) subscale was predicted based on a lower education level. There were no significant predictors of poor mental adjustment in the Cognitive Avoidance (CA) subscale.</p> Conclusion <p>NSCLC patients who were young, unemployed, non-alcohol drinkers, with a lower educational level, and had anxiety were at risk of poor mental adjustment to cancer. Therefore, educational interventions and alleviating anxiety before surgery should be a focus for this group to improve mental adjustment to cancer.</p>