Objective First, to validate the LASA Physical Activity Questionnaire (LAPAQ) by a 7-day diary and a pedometer in older persons. Second, to assess the repeatability of the LAPAQ. Third, to compare the feasibility of these methods. Study design and setting The study was performed in a subsample (n=439, aged 69-92 years) of the Longitudinal Aging Study Amsterdam (LASA). The LAPAQ was completed twice (1998/1999, 1999/2000). Respondents completed a 7-day activity diary and wore a pedometer for 7 days (1999/2000). Results The LAPAQ was highly correlated with the 7-day diary (r=0.68, P<.001), and moderately with the pedometer (r=0.56, P<.001). The repeatability of the LAPAQ was reasonably good (weighted kappa: 0.65-0.75). The LAPAQ was completed in 5.7±2.7 min, and 0.5% of the respondents had missing values. Conclusion The LAPAQ appears to be a valid and reliable instrument for classifying physical activity in older people. The LAPAQ was easier to use than the 7-day diary and pedometer.