OBJECTIVES: To develop and evaluate a short version of the 10/66 dementia diagnostic schedule for use in low-income and middle-income countries. DESIGN: Split-half analysis for algorithm development and testing; cross-evaluation of short-schedule and standard-schedule algorithms in 12 community surveys. SETTINGS: (1) The 10/66 pilot sample data set of people aged 60 years and over in 25 international centres each recruiting the following samples: (a) dementia; (b) depression, no dementia; (c) no dementia, high education and (d) no dementia, low education. (2) Cross-sectional surveys of people aged 65 years or more from 12 urban and rural sites in 8 countries (Cuba, Dominican Republic, Peru, Mexico, Venezuela, India, China and Puerto Rico). PARTICIPANTS: In the 10/66 pilot samples, the algorithm for the short schedule was developed in 1218 participants and tested in 1211 randomly selected participants; it was evaluated against the algorithm for the standard 10/66 schedule in 16 536 survey participants. OUTCOME MEASURES: The short diagnostic schedule was derived from the Community Screening Instrument for Dementia, the CERAD 10-word list recall task and the Euro-D depression screen; it was evaluated against clinically assigned groups in the pilot data and against the standard schedule (using the Geriatric Mental State (GMS) rather than Euro-D) in the surveys. RESULTS: In the pilot test sample, the short-schedule algorithm ascertained dementia with 94.2% sensitivity. Specificities were 80.2% in depression, 96.6% in the high-education group and 92.7% in the low-education group. In survey samples, it coincided with standard algorithm dementia classifications with over 95% accuracy in most sites. Estimated dementia prevalences in the survey samples were not consistently higher or lower using the short compared to standard schedule. CONCLUSIONS: For epidemiological studies of dementia in low-income and middle-income settings where the GMS interview (and/or interviewer training required) is not feasible, the short 10/66 schedule and algorithm provide an alternative with acceptable levels of performance.