The use of four types of psychological state words (physiological, emotional, desire, and cognitive) during mother-child play sessions at ages 3, 4, and 5 years was examined in 30 children diagnosed with delayed expressive language at 24-31 months and 15 age-matched comparison children with typical development. The children's mean length of utterance, total words uttered, lexical diversity, and use of propositional complements were assessed. The late talkers used significantly more physiological state words at ages 3 and 4, but the two groups did not differ in their use of physiological state terms at age 5. The late talkers used significantly fewer cognitive words than the comparison children at each age. The mothers of the late talkers made significantly fewer references to cognitive states than the mothers of the comparison children at each age. The delay in the emergence of cognitive state words in the preschool years may affect other aspects of late talkers' cognitive and social development.