Data are reported from a national probability sample used to norm the Language Development Survey (LDS; L. Rescorla, 1989) and the Child Behavior Checklist for Ages 1 1/2-5 (CBCL/1 1/25; T. M. Achenbach & L. Rescorla, 2000). Participants were 278 children 18 to 35 months old who were highly diverse in socioeconomic status (SES), ethnic composition, and language background. Vocabulary scores increased markedly with age, were somewhat higher in girls, and were modestly correlated with SES. Children of non-Latino White ethnicity had significantly higher vocabulary scores and mean length of phrases than children of African American or "other" ethnicity (Hispanics/Asians/Native Americans/South Asians/mixed), even when SES was used as a covariate. Rate of language delay, using the cut-off of fewer than 50 words or no word combinations, was lower in the non-Latino White group (4%) than in the other two ethnicity groups (29% and 24%). Correlations between LDS scores and problem scores on the CBCL/1 1/2-5 were low, indicating that language delay and emotional/behavior problems were not closely associated in this general population sample of children 18 to 35 months old.