The subjects of this thesis are decision analysis and receiver operating characteristic (ROC) methodology applied to radiological problems. This thesis is intended for those interested in applying decision analytical techniques in diagnostic radiology, and in medicine in general. Chapter II deals with the theory of decision trees and Markov processes. The basic concepts are briefly explained and a few selected topics are discussed in more detaiL Chapter III describes a decision model for the diagnostic workup and treatment of renovascular hypertension. Chapter IV presents a Markov analysis of the decision whether, and when, to intervene in acute urinary tract obstruction. Chapter V deals with the theory of receiver operating characteristic (ROC) methodology. Basic concepts are explained and a number of selected issues are discussed in detaiL Chapter VI presents an ROC analysis of the assessment of tumor extension in neoplastic disease of the nose, paranasal sinuses, nasopharynx and parapharyngeal space, comparing computer tomography (CT) and magnetic resonance imaging (MRI). Chapter VII presents the results of an ROC analysis of orbital space-occupying lesions comparing the diagnosis made by means of clinical evaluation, computer tomography (CT) and magnetic resonance imaging (MRI). Chapter VIII presents the results of a study on fetal pulmonary maturity testing, involving a number of interesting methodological issues of ROC analysis. A general discussion follows in chapter IX.