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Overdiagnosis is a major potential harm of lung cancer screening; knowing its potential magnitude helps to optimize screening eligibility criteria. The German Lung Screening Intervention Trial ("LUSI") is a randomized trial among 4052 long‐term smokers (2622 men), 50.3 to 71.9 years of age from the general population around Heidelberg, Germany, comparing five annual rounds of low‐dose computed tomography (n = 2029) with a control arm without intervention (n = 2023). After a median follow‐up of 9.77 years postrandomization and 5.73 years since last screening, 74 participants were diagnosed with lung cancer in the control arm and 90 in the screening arm: 69 during the active screening period; of which 63 screen‐detected and 6 interval cancers. The excess cumulative incidence in the screening arm (N = 16) represented 25.4% (95% confidence interval: −11.3, 64.3] of screen‐detected cancer cases (N = 63). Analyzed by histologic subtype, excess incidence in the screening arm appeared largely driven by adenocarcinomas. Statistical modeling yielded an estimated mean preclinical sojourn time (MPST) of 5.38 (4.76, 5.88) years and a screen‐test sensitivity of 81.6 (74.4%, 88.8%) for lung cancer overall, all histologic subtypes combined. Based on modeling, we further estimated that about 48% (47.5% [43.2%, 50.7%]) of screen‐detected tumors have a lead time ≥4 years, whereas about 33% (32.8% [28.4%, 36.1%]) have a lead time ≥6 years, 23% (22.6% [18.6%, 25.7%]) ≥8 years, 16% (15.6% [12.2%, 18.3%]) ≥10 years and 11% (10.7% [8.0%, 13.0%]) ≥12 years. The high proportions of tumors with relatively long lead times suggest a major risk of overdiagnosis for individuals with comparatively short remaining life expectancies. What's new? The reduced lung cancer mortality achieved through low‐dose computed tomography screening must be balanced against the risk of overdiagnosis. In this randomized screening trial with 5 annual screening rounds and a median post‐screening follow‐up of 5.73 years, excess lung cancer incidence represented 25.4% of the screen‐detected cases. The mean pre‐clinical sojourn time was 5.38 years. The probabilities for screen‐detected tumors to have remained asymptomatic for 4 and 12 years in the absence of screening were 48% and 11%, respectively. The findings suggest that individuals with short remaining lifetime are at high risk of being overdiagnosed by low‐dose computed tomography screening. [ABSTRACT FROM AUTHOR]