A new language measure, the Observation of Spontaneous Expressive Language (OSEL), is intended to document spontaneous use of syntax, pragmatics, and semantics in 2–12-year-old children with Autism Spectrum Disorder (ASD) and other communication disorders with expressive language levels comparable to typical 2–5 year olds. Because the purpose of the OSEL is to provide developmental norms for use of language, the first step involves assessment of the scale’s feasibility, validity, and reliability using a sample of 180 2–5 year-old typically developing children. Pilot data from the OSEL shows strong internal consistency, high reliabilities and validity. Once replicated with a large population-based sample and in special populations, the scale should be helpful in designing appropriate interventions for children with ASD and other communication disorders.