In this paper, we discuss an ontology-based system and approach that provides interoperability support for research in, and diagnosis of, human disease. The proposed solution incorporates a prototype for a Generic Human Disease Ontology that contains common general information regarding human diseases. This proposed Generic Human Disease Ontology represents the information in 4 'dimensions': (1) disease types, (2) phenotype (observable characteristics of an organism) or symptoms (3) causes related to the disease, namely genetic causes (genes, gene complexes and DNA regions of interest) and environmental causes (such as stress, family condition, drugs, climate etc.), and (4) treatments available for the disease such as drug therapy, chemotherapy, physiotherapy, psychotherapy, surgery etc. The Generic Human Disease Ontology aims to support also the study of complex disorders caused by many different factors simultaneously e.g. the case of manic depressive disorders. We illustrate how this Generic Human Disease Ontology helps to produce Specific Human Disease Ontologies on request, as support tool for physicians and medical researchers.