Anaplastic lymphoma kinase (ALK) tyrosine kinase inhibitors (TKIs) have shown promising clinical activity in the treatment of non-small-cell lung cancer (NSCLC) that harbors ALK rearrangement. The next-generation ALK-TKI, alectinib, has been reported to have potent efficacy in ALK-positive NSCLC patients including on mutations that confer resistance to crizotinib, which was the first ALK-TKI approved for ALK-positive NSCLC. The efficacy and safety of ALK-TKIs, including crizotinib and alectinib, as the first-line treatment in critically ill patients is unclear. We report one ALK-positive NSCLC patient with poor performance status (PS) and disseminated intravascular coagulation because of respiratory failure and multiple metastases, and experienced the rapid and dramatic response to alectinib without adverse events that can lead to discontinuation and dose reduction of the drug. After a couple of months of treatment with alectinib, radiological review indicated a complete response. The present case is the first reported case of rapid and marked response to alectinib in ALK-positive NSCLC patients who had poor PS and severe organ dysfunction, such as disseminated intravascular coagulation. Further investigation of the safety and efficacy of ALK-TKI for ALK-positive NSCLC patients who are critically ill is warranted.