Objective: To examine the validity of self-reported height and weight data reported over the telephone in the 1997 NSW Health Survey, and to determine its accuracy to monitor overweight and obesity in population surveys.

Method: Self-reported and measured heights and weights were collected from 227 people living in Western Sydney, who had participated in the NSW Health Survey 1997.

Results: Self-reported (SR) weights and heights led to misclassification of relative weight status. BMI, based on measured weights and heights, classified 62% of males and 47% of females as overweight or obese, compared with 39% and 32%, respectively, from self-report.

Conclusions: Caution should be used when interpreting SR height and weight data from surveys, because BMI derived from these is likely to underestimate the true prevalence of overweight and obesity.

Implications: SR data have a place in nutrition monitoring because they are relatively inexpensive and easy to collect. However, classifying people into weight categories on the basis of accepted cut-points, using SR heights and weights, yields inaccurate prevalence estimates. Periodic sub-studies of the validity of SR heights and weights are needed to indicate the extent to which the validity of SR is changing.