Effective verbalization of pain requires progressive cognitive development and acquisition of social communication skills. Use of self-report in pediatric pain assessment assumes children have acquired a capacity to understand and use common words to describe pain. The current investigation documented the language most commonly used by young children to describe pain and the age of onset of use of these words. Two complementary research methodologies were employed. Study 1 used the CHILDES database, an aggregated transcript database of multiple research studies examining spontaneous speech development across childhood. Transcripts of 14 randomly selected studies, yielding a total of 245 child participants ranging in age from 1 to 9 years, were searched for seven English primary pain word-stems: 'ache', 'boo-boo', 'hurt', 'ouch', 'ow', 'pain', and 'sore'. Study 2 surveyed 111 parents of children aged 3 to 6 years old concerning words the children commonly used for pain. Parents rated their children's frequency and age of first use of the seven pain word-stems. Both studies indicated that the most frequently used word-stems were 'hurt', 'ouch', and 'ow'. These words first emerged in children's vocabularies as early as 18 months of age. The word-stem 'pain' was used relatively infrequently and gradually emerged in children's vocabularies. The findings indicate that young children rely on a select number of words to describe pain, with these words appearing in children's vocabularies at an early age. These results have implications for developmentally appropriate pain assessment in young children.