The objectives of this study were to report the inter-rater reliability of the Brief Psychiatric Rating Scale (BPRS 4.0) and the Groningen Social Disabilities Schedule (GSDS-II) as assessed in a randomized controlled trial on the effectiveness of psychiatric day hospitals spanning five sites in countries of Central and Western Europe. Following brief training sessions, videotaped BPRS-interviews and written GSDS-vignettes were rated by clinically experienced researchers from all participating sites. Inter-rater reliability often proved to be poor for items assessing the severity of both psychopathology and social dysfunction, but findings suggest that both instruments allow for the assessment of the presence or absence of specific psychopathological symptoms or social disabilities. Inter-rater reliability at subscale level proved to be good for both instruments. Results indicate that, with a brief training session and proper use of the instruments, psychopathology and social disabilities can be reliably assessed within cross-national research studies. The results are of particular interest given that the need to conduct cross-national multi-site studies including countries with different cultural backgrounds increases.