ABSTRACTStructured diaries describing the activity of three people with mental handicaps were kept by direct‐care staff and compared with results of simultaneous direct observation using five‐second momentary time‐sampling. Item‐by‐item agreement on main activity in five‐minute time blocks ranged from 41 to 72 per cent. Even averaged across three‐hour sessions substantial inaccuracy remained. These results suggest great caution is needed in using diaries as a source of ev