Twelve typical carcinoid tumors (TCT) and eight atypical (malignant) carcinoid tumors (ACT) of the lung were studied for quantitative DNA content by image analysis in order to identify prognostic features. No correlation of any histologic variables of the TCTs and ACTs with abnormal DNA content were noted. Furthermore, it was concluded that although abnormalities of DNA content, particularly aneuploidy, are common in ACTs, DNA ploidy cannot be used independently to assess malignant potential.