The Structured Interview for Competency and Incompetency Assessment Testing and Ranking Inventory (SICIATRI) is a structured interview guide to assess the competency for giving informed consent to treatment among psychiatric and medical patients. The competency levels of 48 psychiatric and medical inpatients were assessed by SICIATRI. A relatively high- inter-rater reliability of the SICIATRI items (over half of the items had kappa > or = .60) and concurrent validity (sensitivity = .83, specificity = .67 as measured against the global judgement of competency rating by the attending physician) were obtained. In addition to its brevity (it takes about 20 minutes to complete), these findings may warrant application of this instrument in a clinical setting.