Abstract: In the present paper, we propose a novel recognition method of pulmonary nodules (possible lung cancers) in thoracic CT scans. Pulmonary nodules and blood vessels are represented by 3-D deformable spherical and cylindrical models. The validity of these object models are evaluated by the probability distributions that reflect the results of the statistical anatomical analysis of blood vessel trees in human lungs. The fidelity of the object models to CT scans are evaluated by five similarity measurements based on the differences in intensity distributions between the CT scans and templates produced from the object models. Through these evaluations, the posterior probabilities of hypotheses that the object models appear in the CT scans are calculated by use of the Bayes theorem. The nodule recognition is performed by the maximum a posterior estimation. Experimental results obtained by applying the proposed method to actual CT scans are shown.