Birth defects (BDs) are a serious public health problem in Mexico. The objective of this paper was to identify the frequency of newborns (NBs) that are born small for gestational age with a birth defect.A cross-sectional study of NBs from hospitals part of the Mexican Institute of Social Security in Chihuahua, Mexico, was conducted. NBs were classified according to the presence or absence of a BD and according to their weight percentile using regional standards of birth weight.NBs diagnosed with (n = 263) or without BDs (n = 64,626) were included in this study. A greater proportion of NBs small for gestational age were identified in cases involving BDs (20%), compared with NBs without BDs (9%). Moreover, the average decrease in birth weights of NBs with BDs associated with their digestive system was 210 grams (95% confidence interval [CI], -436/-12), with their genital organs 440 grams (95% CI, -730/-151), involving chromosomal abnormalities 230 grams (95% CI, -435/-26), or with their musculoskeletal system 289 grams (95% CI, -43/-147) according to the gestational age, sex, and condition of the NB (p < 0.05).A greater proportion of NBs with BDs were associated with a low birth rate for their gestational age. In addition, some BDs were found to be associated with an impaired birth weight more often than others This suggests that clinical decisions regarding NBs with congenital defects and a lower birth weight for their gestational age should be diagnosed and treated for additional nutritional considerations as needed. Birth Defects Research (Part A), 2011. © 2011 Wiley-Liss, Inc.