Recent technological advances in thoracic radiology and surgery have altered the types of lung specimens handled by cytologists and surgical pathologists. Increasing numbers of individuals with small peripheral adenocarcinomas undergo minimally invasive diagnostic procedures and, in some instances, minimally invasive surgical procedures. The pathologist's role in early lung adenocarcinoma research is central, as clinical and investigational studies depend more than ever on subtle pathologic distinctions. Establishing a diagnosis of malignant neoplasm on samples from fine-needle aspiration, core biopsy, or frozen section is fraught with new considerations, and surgically resected adenocarcinomas must be typed according to the recently revised World Health Organization classification. Familiarity with small glandular proliferations, including the putative precursor lesion atypical adenomatous hyperplasia, will prevent misdiagnoses and untoward impact on tumor staging, therapy, and outcome studies.