Since the compilation of the first dictionaries in English, lexicographers have been interested in chronicling the language of the criminal underworld. Over time, many methods of data-collection have been employed. One recent method is the sociolinguistic interview. In this study, the sociolinguistic interview was used to collect lexical information from inmates in all New Zealand prisons. The challenges of interviewing in prison are discussed, together with the ways the interviews were formulated to overcome these challenges and produce a large amount of reliable data.