OBJECTIVES: This study investigated predictors of delayed language development at 18 months of age in a large population cohort of Norwegian toddlers. METHODS: Data were analyzed on 42,107 toddlers. Language outcome at age 18 months was measured using a standard parent report instrument, the Ages and Stages Questionnaire, communication scale. Confirmatory factor analysis was conducted on the Ages and Stages Questionnaire items. A theoretically derived set of child, family, and environmental risk factors were used to predict delayed language development at age 18 months using Generalized Estimating Equation. RESULTS: A number of child factors, including being a boy, low birth weight or gestational age, or a multiple birth child were all significantly associated with low scores on the language outcome at age 18 months. Maternal distress/depression and low maternal education, having older siblings, or a non-Norwegian language background also predicted low scores on the language outcome at age 18 months. Overall, estimated variance in language outcome explained by the model was 4% to 7%. CONCLUSIONS: A combination of early neurobiological and genetic factors (e.g., male gender, birth weight, and prematurity) and concurrent family variables (e.g., maternal distress/depression) were associated with slower language development at age 18 months. This finding replicated previous research conducted on slightly older language-delayed 2 year olds but also detected the importance of factors related to family resources for the first time in this younger age group. Despite this finding, most of the variability in language performance in this cohort of 18 month olds remained unexplained by the comprehensive set of purported risk factors.