The German Health Interview and Examination Survey for Children and Adolescents (KiGGS) is a nationwide representative survey on the health status of German children and adolescents in 2003 to 2006 (N = 17 642; aged 0-17 years).3 We used the public use file of KiGGS, which does not contain any personal identifiers; thus, ethical approval was not required. Data from all participants aged 3 to 17 years (n = 13 488) were included. The outcome of interest was lifetime diagnosis of ADHD on the basis of medical or psychological examination as reported in standardized parental interviews conducted by trained interviewers.3 In Germany, ADHD is generally diagnosed according to the International Statistical Classification of Diseases, 10th Revision criteria of “hyperkinetic disorder” that largely correspond with the criteria of the Diagnostic and Statistical Manual of Mental Disorders (Fourth Edition, Text Revision) definition of ADHD combined subtype.1 Primary exposures of interest were self-reported physician-diagnosed GDM (absent/present) and SEP classified as low, medium, or high based on parental education, professional qualification, professional status, and family net income.4 Additionally, age, sex, and a broad set of environmental exposures in the prenatal/perinatal period and in infancy such as breastfeeding (ever vs never fully breastfed); postnatal health problems including breathing problems, maladaptation, infections, jaundice, low birth weight and/or premature delivery, and inpatient treatment (present/absent); maternal smoking/drinking during pregnancy (ever/never); and physician-diagnosed atopic eczema5 (ever/never) were considered as competing risk factors in multivariate logistic regression models based on 11 222 observations without missing data. Additive and multiplicative interaction was explored by combining SEP and GDM into 1 variable (reference: no GDM, high SEP). To assess the mode of interaction (additive or multiplicative), we compared the expected odds ratios (ORs) on the basis of single exposures with the observed OR of combined exposure to GDM and SEP.6 Data were analyzed using Stata (StataCorp).