Objectives Lung cancer CT screening can reduce lung cancer mortality, but high false-positive rates may cause adverse psychosocial consequences. The aim was to analyse the psychosocial consequences of false-positive lung cancer CT screening using the lung cancer screening-specific questionnaire, Consequences of Screening in Lung Cancer (COS-LC). Design and setting This study was a matched cohort study, nested in the randomised Danish Lung Cancer Screening Trial (DLCST). Participants Our study included all 130 participants in the DLCST with positive CT results in screening rounds 2-5, who had completed the COS-LC questionnaire. Participants were split into a true-positive and a false-positive group and were then matched 1:2 with a control group (n=248) on sex, age (±3 years) and the time of screening for the positive CT groups or clinic visit for the control group. The true positives and false positives were also matched 1:2 with participants with negative CT screening results (n=252). Primary outcomes Primary outcomes were psychosocial consequences measured at five time points. Results False positives experienced significantly more negative psychosocial consequences in seven outcomes at 1 week and in three outcomes at 1 month compared with the control group and the true-negative group (mean &circ;† score >0 and p<0.001). True positives experienced significantly more negative psychosocial consequences in one outcome at 1 week (mean &circ;† score 2.86 (95% CI 1.01 to 4.70), p=0.0024) and in five outcomes at 1 month (mean &circ;† score >0 and p<0.004) compared with the true-negative group and the control group. No long-term psychosocial consequences were identified either in false positives or true positives. Conclusions Receiving a false-positive result in lung cancer screening was associated with negative short-term psychosocial consequences. These findings contribute to the evidence on harms of screening and should be taken into account when considering implementation of lung cancer screening programmes. Trial registration number NCT00496977.