To assess whether anthropometric data, routinely collected as part of the Scottish Child Health Surveillance System (CHSP-PS, pre-school children; CHSP-S, school age children) could provide a means of monitoring/surveillance for obesity and undernutrition at national and health board level. A survey of 15 health boards and both surveillance systems to identify the nature of data collected, format of data, and extent to which data were accessible (e.g., via Information and Statistics Division of the Common Services Agency). Measurements of weight and height collected as part of the CHSP-PS and CHSP-S were extracted from ISD. They were then audited and missing values or implausible values quantified, and degree of dispersion of values used as an index of quality of measurements. Health Board Child Health Surveillance Systems and Information and Statistics Division, Edinburgh. Data on height and weight are currently available for 9 health boards for pre-school children and 4 health boards for school age children. This represents coverage of around 80% of the pre-school child population. Analysis of a data extract from the 39-42 month check in 1998/99, used as an example, revealed that 8% of weight and height data were missing, and approximately 1% were implausible measures. Population and health board level estimates of prevalence of obesity and undernutrition were possible and are presented. Data on height and weight are routinely collected in school age children in all health boards, however only four health boards have growth data electronically available via the school CHSP. Growth data routinely collected as part of child health surveillance for Scotland can be used to estimate population prevalence of undernutrition and obesity. These can in turn be used to monitor trends at local and national level, to monitor achievement in relation to public health targets, identify risk factors and high risk groups, and to follow cohorts over time. We describe a system of surveillance for undernutrition and obesity and identify its strengths and weaknesses.