Background: Adenocarcinoma is the most common primary lung malignant tumor. However, pulmonary carcinoid tumorlets are rare neuroendocrine tumors, and the coexistence of adenocarcinoma and pulmonary carcinoid tumorlets is extremely rare. Herein, we describe a case of lung adenocarcinoma complicated with carcinoid tumorlets.Case presentation: A 71-year-old female patient was admitted to the hospital after physical examination, multiple micronodules were in the inferior lobe of the left lung and right lung for 2 years, and a tumor was in the superior lobe of the left lung for 1 month. The patient underwent resection of the superior lobe of the left lung and wedge resection of the inferior lobe of the left lung by Video-assisted Thoracoscopic Surgery(VATS). The pathology of the superior lobe of the left lung was adenocarcinoma (pathological stage pT1cN0M0, IA3 stage), and the pathology of the inferior lobe of the left lung was carcinoid tumorlets. The patient was discharged from the hospital one week after the operation and recovered well after follow-up without recurrence.Conclusions: The lack of understanding of carcinoid tumorlets in the clinic causes their misdiagnosis or missed diagnosis. At the same time, the lack of understand also suggests that we should pay attention not only to mass-type lung tumors but also to pulmonary micronodules.