We conducted this study to identify the risk for second primary malignancy (SPM), especially for second primary extrapulmonary malignancy (SPEM), in resected stage I lung cancer patients.Resected stage I lung cancer patients were retrospectively enrolled from the SEER database (2008-2017). Standardized incidence ratio (SIR) was used to evaluate the relative risk of SPM of patients as compared to general population. Competing risk model was utilized to identify the risk factors for SPEM of increased risk (rSPEM). A simplified nomogram based on the factors was developed to stratify patients at different risks of rSPEM.A total of 14,495 patients were enrolled, and 1779 (12.27%) patients developed SPM during follow-up, of which 896 (50.37%) were SPEM. Enrolled patients had higher risk of SPM than general population (SIR: 1.92, 95% CI: 1.83 - 2.01). The yearly morbidity of SPM was about 3% - 4% over time. The three most frequent SPEM were prostate cancer, breast cancer, and urinary bladder cancer. The competing-risk multivariable analysis showed that increasing age, male, and white race were independent risk factors for rSPEM. The simplified nomogram showed favorable performance in stratifying patients at different risks of rSPEM (P < 0.001).The risk of SPM in stage I lung cancer patients was high. Risk factors for rSPEM were identified and the corresponding simplified nomogram based on the risk factors could discriminate patients at different risks well. The nomogram might help physicians to make more appropriate screening strategy for the SPEM.Copyright © 2023 Elsevier B.V. All rights reserved.