Despite the importance of measuring weight and height at well-child visits, there are limited data on frequency of anthropometric documentation. The authors aimed to identify characteristics associated with missing weight and height documentation at preventive visits for children. Among preventive visits for children from birth to 18 years old, recorded in the National Ambulatory Medical Care and National Hospital Ambulatory Medical Care Surveys for 2005-2009, the authors found that 20.8% had missing weight and/or height (n = 19,033) documentation. Compared with infants younger than 2 years, school-age children (odds ratio [OR] = 1.30; 95% confidence interval [CI] = 1.03-1.64), and adolescents (OR = 1.61; 95% CI = 1.26-2.04) were more likely to lack documentation. Missing documentation was also more likely for visits with nonphysicians (OR = 4.53; 95% CI = 3.17-6.48) and nonpediatricians (OR = 2.63; 95% CI = 2.02-3.41) compared with pediatricians. Efforts to improve weight and height surveillance should be directed to clinics in which midlevel providers and nonpediatric physicians are caring for school-age children and adolescents.