The authors introduce a screening instrument that assesses cognitive-function domains across adulthood over the telephone. The authors administered the Cognitive Telephone Screening Instrument (COGTEL) to 81 younger adults (M = 25.6 years) and 83 older adults (M = 66.9 years). Each participant completed the COGTEL twice, once over the telephone and once in a face-to-face assessment. The authors (a) analyzed the degree of agreement between face-to-face and telephone COGTEL scores, (b) developed a COGTEL Total score that reflects global cognitive functioning, and (c) examined concurrent validity. The method of administration did not largely influence mean levels, rank orders, or factor structure as revealed by confirmatory factor analysis. Moreover, age differences were not modulated by the form of administration. The distribution of COGTEL Total scores followed a Gaussian function, which prevents COGTEL from being limited by ceiling effects. The results provide evidence for the validity and reliability of the COGTEL to assess cognitive functioning in large-scale epidemiological studies, longitudinal studies, and clinical follow-up among healthy adults.