The objective of this study was to examine factors associated with the validity of self-reported anthropometric measures. The authors selected 726 adults, aged 40 or older, living in the greater metropolitan region of São Paulo, Brazil. Self-reported weights and heights obtained from telephone interviews were compared to values measured directly by means of a multicenter survey. Mean differences (+/-SD) between self-reported and measured weights and heights among men were 0.54 (+/-0.30kg) and 1.98 (+/-0.31cm); while among women, they were -0.48 (+/-0.23kg) and 3.97 (+/-0.28cm), respectively. Sensitivity and specificity to diagnose obesity were 71% and 98% for males, and 78% and 96%, for females, respectively. There was good agreement between measured and self-reported weights and body mass index (BMI) among both sexes, however, self-reported height was less reliable. Self-reported weight and height obtained from telephone interviews are valid to estimate the obesity prevalence in this population, although systematic bias was found. Thus, it is desirable that researchers develop their own equations depending on the population being studied.