There is still a striking lack of homogeneity in the terminology and classifications used in the registration of psychiatric consultation-liaison (C-L) data. Nowadays, the need for standardization of C-L data is greater than ever. Each registration consists of two components: the items and their categories. The present authors distinguish three levels of C-L data: fundamental, epidemiologic, and clinical-educational. A comprehensive proposal for standardization of such items and categories is presented, both on the fundamental and on the epidemiologic level. Data on 2657 consultations carried out by the Netherlands Consortium for C-L Psychiatry (NCCP) and from a literature review of 48 C-L reports serve to illustrate and as a supply for a large database. Various characteristics of the general hospital and of the C-L service are considered to be fundamental, that is, should be presented in each C-L publication. The epidemiologic data are divided into eight groups: sociodemographics, referral characteristics, history, diagnoses, diagnostic recommendations, ward management, discharge and aftercare management, and termination data. Finally, definitions and decision rules are given.