The purpose of this study was to assess the effects of an anticholinergic (trihexyphenidyl) antiparkinsonian medication on the Mini-Mental State Examination (MMSE) and the Cambridge Cognitive Examination (CAMCOG) scores in long-term institutionalized elderly patients with schizophrenia. Seventeen schizophrenic (DSM-III-R) inpatients on long-term medication who had received trihexyphenidyl for at least 6 consecutive months were compared for MMSE scores, CAMCOG scores, and other demographic and clinical variables with 14 patients not receiving any anticholinergic agent for the same time period. Results showed that age, years of education, illness duration, length of current hospital stay, the Manchester Scale scores, and chlorpromazine daily equivalent dose in mg were not different in the two groups compared. Extrapyramidal signs such as tremor, rigidity, and bradykinesia were more frequent in trihexyphenidyl receivers. The scores of MMSE (p ≤ .007) and CAMCOG (p ≤ .005) and CAMCOG subscales of orientation (p ≤ .03), language (p ≤ .01), and memory (p ≤ .002) were significantly lower among trihexyphenidyl receivers, as was the Social and Occupational Functioning Assessment Scale score (p ≤ .05). In addition, the MMSE and CAMCOG scores were significantly lower for patients receiving 10 mg of trihexyphenidyl a day compared with those receiving 5 mg/day and nonusers. It is suggested that trihexyphenidyl in usual clinical doses may impair total MMSE and CAMCOG scores as well as some of the CAMCOG subscales in this patient population. However, only a prospective study, preferably double-blind and controlled, with measures of change will validate this conclusion.