Examination of sputum is the least invasive method of obtaining a cytologic diagnosis in a patient suspected of harboring lung cancer. Cytologic diagnosis has advanced to a point where it is of comparable value to histology. The authors discuss the sensitivity, specificity, reliability, and pitfalls of sputum cytology as well as the role it plays in screening of early lung cancer. The advantages and shortcomings of sampling and cytopreparatory techniques are also reviewed. Concluding remarks outline future developments in sputum cytology.