This study explored retention of idioms and novel (i.e. newly created or grammatically generated) expressions in English-speaking girls following exposure only once during a conversation. Our hypothesis was that idioms, because of their inherent holistic, nonliteral and social characteristics, are acquired differently and more rapidly than novel utterances. Two age groups of typically developing girls, 8-9 and 12-14-year-olds, were exposed to low-frequency idioms and matched novel expressions within a conversational context. Recognition and comprehension of target and nontarget idioms and novel expressions were compared following the exposure period. Ratings were obtained from participants and parents about idiom familiarity. Participants recognized significantly more target idioms than novel expressions following exposure and scored higher on comprehension of target idioms than nontarget idioms. Recognition scores did not differ significantly by age groups, but older children performed significantly better on comprehension of target idioms. (Contains 3 tables.)