This study compared teachers' ratings of behavioral and emotional problems on the Teacher's Report Form for general population samples in 21 countries (N = 30,957). Correlations between internal consistency coefficients in different countries averaged 0.90. Effects of country on scale scores ranged from 3% to 13%. Gender effects ranged from less than 1% to 5%, and age effects were all less than 1%. With great consistency across countries, scores were higher for boys than for girls on eight scales: Total Problems; Externalizing; the Attention Problems, Rule-Breaking Behavior, and Aggressive Behavior syndromes; and "Diagnostic and Statistical Manual" (DSM)-oriented Attention Deficit Hyperactivity Problems, Oppositional Defiant Problems, and Conduct Problems. Correlations between mean item ratings in different countries averaged 0.74. Teacher's Report Form results were thus similar across 21 very diverse countries, despite differences across these countries in school systems, models of pedagogy, and curricula. (Contains 2 figures and 4 tables.)