To facilitate the systematic description of catatonic signs, we developed a catatonia rating examination, rating scale and screening instrument. We constructed a 23-item rating scale and a truncated 14-item screening instrument using operationalized definitions of signs ascribed to catatonia in published sources. Inter-rater reliability was tested in 44 simultaneous ratings of 28 cases defined by the presence of > or = 2 signs on the 14-item screen. Inter-rater reliability for total score on the rating scale was 0.93, and mean agreement of items was 88.2% (SD 9.9). Inter-rater reliability for total score on the screening instrument was 0.95, and mean agreement of items was 92.7% (SD 4.9). Diagnostic agreement was high based on criteria for catatonia put forth by other authors. Seven per cent (15/215) of consecutively admitted patients to an academic psychiatric in-patient facility met criteria for catatonia. It is concluded that catatonia is a distinct, moderately prevalent neuropsychiatric syndrome. The rating scale and screening instrument are reliable and valid. Their use facilitates diagnosis, treatment protocols, and cross-study comparisons.