This pilot study evaluated variability in physical activities and the correlations between walking, two types of postural transitions, and falls efficacy with an ambulatory activity monitor. An 11-subject convenience sample wore the monitor for 2 consecutive days; in addition, 7 subjects carried the monitor on 1 day of the following week. Demographic characteristics of the sample were age: mean +/- standard deviation [SD] = 87.8 +/- 2.5 yr, body mass index: mean +/- SD = 25.3 +/- 2.1 kg/m(2), and Mini-Mental State Examination score: mean +/- SD = 27.5 +/- 2.0. Analyzed movements were sit-to-stand (SiSt) and stand-to-sit postural transitions, dynamic activity (walking), and static behavior (sitting, standing, lying). Significant correlations were found for the SiSt transition duration (TD) between days (intraclass correlation coefficient = 0.78). No differences were found between the durations of sitting (p = 0.8), lying (p = 0.72), standing (p = 0.06), and walking (p = 0.6). These parameters showed highly variable correlation coefficients. A significant correlation was observed between falls efficacy and SiSt measures (r = 0.84, p < 0.01, df = 9). We reliably determined the SiSt TD after subjects wore the monitor for 1 day in the home environment. Poor correlations between 2 consecutive measurement days for dynamic and static activity underline the necessity of recording further days to assess physical activity levels in the geriatric population.