Objective: Until now the ALK status in CTCs isolated from lung cancer patients has not been characterised. We assessed the ALK status in CTCs detected in lung cancer patients and correlated the results to the ALK status defined in the corresponding tumour tissue. Method: 87 lung adenocarcinoma patients showing CTCs isolated using the Isolation by Size of Epithelial Tumour cell method were screened for their ALK status both in tumour samples and in CTCs. ALK break-apart fluorescence in situ hybridisation (FISH) and immunochemistry using an anti-ALK antibody were done on CTCs and compared with results obtained on corresponding tissue specimens. Results: 5 patients showed ALK-gene rearrangement and strong ALK protein expression in CTCs and corresponding tumour samples. Negative results were found for 82 patients in CTCs and corresponding tumour samples. Conclusion: We demonstrate that the ALK status can be determined in CTCs from lung cancer patients both by immunocytochemistry and FISH analysis. A strong correlation was found for the ALK status obtained from corresponding tissue specimens. These results favour non-invasive, ALK-gene status pre-screening on a routine basis on CTCs isolated form lung cancer patients and open new avenues for real-time monitoring for adapted targeted therapy.