The severity of left lung apical nodules depends on the individual case, as there are benign and malignant causes of left lung apical nodules. Benign lesions are generally not serious, while malignant lesions are serious and their prognosis depends on a number of factors. Benign lesions generally include benign tumors, pneumonia, tuberculosis, and pulmonary hemangiomas, which can be cured with active treatment. Malignant lesions generally include primary lung cancer, metastatic malignant tumors, etc., which can endanger the patient’s life and require timely discussion with the doctor about treatment options and early surgical resection. The severity of small nodules in the posterior apical segment of the upper lobe of the left lung is also related to a number of factors. Generally speaking, the prognosis of patients with acute onset, benign lesions and timely treatment is generally good and not serious; if the disease is chronic and progressive, malignant lesions, and untimely treatment, the prognosis is worse and more serious as the disease may invade multiple organs and cause functional damage to multiple organs. Therefore, if small nodules are found in the posterior apical segment of the upper lobe of the left lung, one should go to the hospital in time to find out the cause of the disease as soon as possible and treat the symptoms in order to avoid delaying the disease.