Background The Clock-in-the-Box is a rapid (2-minute) cognitive screening tool. The purpose of this study was to compare the Clock-in-the-Box with the Mini-Mental State Exam and neuropsychologic tests; to determine Clock-in-the-Box score normative values by age and education group; and to determine if the Clock-in-the-Box score is associated with measures of physical function. Methods Community-dwelling older participants in the Boston area were recruited for a prospective, longitudinal study in which they completed a variety of cognitive and functional assessments. Results At baseline, participants (n=798; mean age [± standard deviation]=78.2 [±5.5] years; 14 [±3] mean years of education) completed in-home assessments of cognition (Clock-in-the-Box and Mini-Mental State Exam), measures of independent function (Activities of Daily Living and Instrumental Activities of Daily Living), and measures of physical function (Short Physical Performance Battery). The mean Mini-Mental State Exam score was 27.1 (±1.6; range 0-30 [0 worst]), and the mean Clock-in-the-Box score was 6.2 (±1.6; range 0-8 [0 worst]). Performance on the Clock-in-the-Box was correlated (Spearman) with the Mini-Mental State Exam (r =0.49, P <.001) and neuropsychologic measures (r =0.37-0.50; P <.001). Higher Clock-in-the-Box score was significantly associated with no difficulty in Activities of Daily Living (χ2 = 39.6, P <.001) and Instrumental Activities of Daily Living (χ2 = 35.5, P <.001). In addition, higher Clock-in-the-Box scores were associated with higher scores on the Short Physical Performance Battery (F=5.4, P <.001). Conclusion The Clock-in-the-Box is a brief cognitive screening test that is correlated with the Mini-Mental State Exam, neuropsychologic tests, and measures of independent and physical function in community-dwelling older adults.