Cognitive impairment in psychosis is closely related to functional outcome, so research into psychotic disorders is focusing most effort on treatments for improving cognition. New treatments must show not only an improvement on neuropsychological tests but also in co-primary measures of cognition. The cognitive assessment interview (CAI) is an interview-based measure of cognition which assesses the impact of cognitive deficits in patients’ daily lives. Information obtained from patients and their relatives is integrated into a rater composite score. This study examines the validity of the CAI (adapted to Spanish, CAI-Sp) as a screening instrument for cognitive impairment, compared to an objective test of cognitive functioning. The psychometric properties of the CAI-Sp and its association with clinical dimensions are also explored. Eighty-one patients with a psychotic disorder and 38 healthy controls were assessed using the CAI-Sp and the screen for cognitive impairment in psychiatry (SCIP-S). Patients also underwent a clinical assessment. Poorer cognitive functioning as assessed with the CAI-Sp was associated to illness severity, specifically positive, negative and disorganised syndromes. Binary logistic regression showed that the CAI-Sp was able to detect cognitive impairment in patients, when considering CAI-Sp patient and informant information and CAI-Sp rater scores. The CAI-Sp was found to be a valid and reliable scale to assess cognitive functioning in the context of its impact on daily living. Given its ease and speed of application, the CAI-Sp could prove useful in clinical practice, though not a substitute of objective cognitive testing.