This paper reports data from four studies using the Language Development Survey (LDS), a vocabulary checklist designed for use as a screening tool for the identification of language delay in 2-year-old children. A survey completed by the parent in about 10 min, the LDS displayed excellent reliability as assessed by Cronbach's alpha and test-retest techniques. Total vocabulary score as reported on the LDS was highly correlated with performance on Bayley, Reynell, and Preschool Language Scale expressive vocabulary items. The LDS was found to have excellent sensitivity and specificity for the identification of language delay, with a criterion of fewer than 50 words or no word combinations at 2 years yielding very low false positive and false negative rates. Data from three of these studies demonstrate the utility of the LDS as a screening tool for children attending public and private pediatric practices. Prevalence data using the LDS are reported comparing three different severity cutoffs for more than 500 children in seven survey samples.