Purpose: Two approaches commonly used for estimating prevalence of language disorders in families were compared. The 1st involved examining a subset of language items from an investigator-based interview used to record parental information on the language and literacy difficulties in relatives. The 2nd was the direct assessment of ability in immediate family using a battery of standardized verbal ability, language, and literacy assessments. Method: Using these 2 methods, the prevalence of language and literacy disorders was investigated in the immediate family (n = 271) of 93 children with a history of SLI (mean age 13;11 years). Results: The overall proportion of relatives with reported language or literacy difficulty was similar for both methods (34.5% for reported difficulties compared with 35% on direct assessment). The present study further explored maternal, paternal, and sibling prevalence rates and strength of agreement between parental interview and direct assessment. When a low cutoff score was used, good agreement (of true negatives and true positives) for reading and spelling difficulties and expressive language between the 2 types of case identification method was found. Conclusions: Parents can be effective identifiers when the impairment is severe (below 2 "SDs" from the population mean). Poor agreement was observed between report and assessment of receptive language difficulties. (Contains 7 tables and 1 figure.)