Nosologic classification of diseases is accessible on line in a computer system. A computer data base has records of discriminating features, consistent features and variable features of known afflictions. The features are in classification domains which include a phenomenologically classified domain, classified by listing commonly agreed on observations and distinguishing between entities based on these observations. Other classification domains are anatomically classified, pathologically classified by the gross of microscopic pathologic anatomy, revealed by either traditional pathologic study or imaging. One of the classification domains is pathophysiologically, by demonstrating altered chemical or electrophysiological parameters. At least one of the classification domains is classified ethiologically by cause.